Make no. of communities per pagination / expansion configurable

Adds new config settings for no. of communities to display on the
home page & community-list page.

Resolves #1749, resolves #1750

src/config/app-config.interface.ts

@@ -31,6 +31,7 @@ interface AppConfig extends Config {
   defaultLanguage: string;
   languages: LangConfig[];
   browseBy: BrowseByConfig;
+  browseCommunities: BrowseCommunitiesConfig;
   item: ItemConfig;
   collection: CollectionPageConfig;
   themes: ThemeConfig[];