Refactor merged field structure

Here is the new model:

+-----------------------------+
|          Structure          |
+-----------------------------+
| +createFromDataboxes()      |
| getAllFields()              |
| getUnrestrictedFields()     |
| getPrivateFields()          |
| getFacetsFields()           |
| getThesaurusEnabledFields() |
| getDateFields()             |
|- - - - - - - - - - - - - - -|
| add()                       |
| get()                       |
| typeOf()                    |
| isPrivate()                 |
+-------+-+-+-----------------+
        | | |          +---------------------+
        | | +--------> |        Field        |
        | |            +---------------------+
        | |            | getName()           |
        | |            | getType()           |
        | |            | isXXX()             |
        | |            | getThesaurusRoots() |
        | |            +---------------------+
        | |
        | |            +-------+
        | +----------> | Field |
        |              +-------+
        |
        |              +-------+
        +------------> | Field |
                       +-------+

It was driven by the following use cases:
- Get list of facets (only searchable fields)
- Get list of fields with concept inference
- Get list of all fields
    - Splitted in private / public fields (to define mapping)
- Get all date fields
- Get field type
    - To apply sanitization rules
    - To define mapping
- Check if concept inference enabled
- Check if the field is searchable
- Check if the field is a facet
- Check if the field is private
- Dereference field from label (still to be done)

(The last two UCs are new)

Also removed old code from legacy search engines.

[#PHRAS-500]

lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/Structure.php

@@ -0,0 +1,99 @@
+<?php
+
+namespace Alchemy\Phrasea\SearchEngine\Elastic\Structure;
+
+use Alchemy\Phrasea\SearchEngine\Elastic\Mapping;
+
+class Structure
+{
+    private $fields = array();
+    private $date_fields = array();
+    private $thesaurus_fields = array();
+    private $private = array();
+    private $facets = array();
+    private $aliases = array();
+
+    public static function fromDataboxes(array $databoxes)
+    {
+        $structure = new self();
+        foreach ($databoxes as $databox) {
+            foreach ($databox->get_meta_structure() as $fieldStructure) {
+                $field = Field::createFromLegacyField($fieldStructure);
+                $structure->add($field);
+            }
+        }
+        return $structure;
+    }
+
+    public function add(Field $field)
+    {
+        $name = $field->getName();
+        if (isset($this->fields[$name])) {
+            $this->fields[$name]->mergeWith($field);
+        } else {
+            $this->fields[$name] = $field;
+        }
+
+        if ($field->getType() === Mapping::TYPE_DATE) {
+            $this->date_fields[$name] = $field;
+        }
+        if ($field->isPrivate()) {
+            $this->private[$name] = $field;
+        }
+        if ($field->isFacet()) {
+            $this->facets[$name] = $field;
+        }
+        if ($field->hasConceptInference()) {
+            $this->thesaurus_fields[$name] = $field;
+        }
+    }
+
+    public function getAllFields()
+    {
+        return $this->fields;
+    }
+
+    public function getUnrestrictedFields()
+    {
+        return array_diff_key($this->fields, $this->private);
+    }
+
+    public function getPrivateFields()
+    {
+        return $this->private;
+    }
+
+    public function getFacetFields()
+    {
+        // TODO should we only return searchable fields?
+        return $this->facets;
+    }
+
+    public function getThesaurusEnabledFields()
+    {
+        return $this->thesaurus_fields;
+    }
+
+    public function getDateFields()
+    {
+        return $this->date_fields;
+    }
+
+    public function get($name)
+    {
+        return isset($this->fields[$name]) ?
+                     $this->fields[$name] : null;
+    }
+
+    public function typeOf($name)
+    {
+        return isset($this->fields[$name]) ?
+                     $this->fields[$name]->getType() : null;
+    }
+
+    public function isPrivate($name)
+    {
+        return isset($this->private[$name]) ? true :
+               isset($this->fields[$name])  ? false : null;
+    }
+}