Use Haystack search indexes

[Mognom]

Use Haystack for all search indexes instead of Whoosh.
Currently only Whoosh, Solr and ElasticSearch backends are supported for Wirecloud.

[aarranz]

Missing tasks:

• Provide a backwards compatible resetsearchindexes command in addition to the rebuild_index command provided by haystack. Restore resetsearchindexes documentation and state that it will be removed in WireCloud v1.3.
• Use previous index names (e.g. catalogueresource should be resource)
• restore # noqa comments
• Create a WirecloudSignalProcessor class that search models to be indexed and always use that signal processor (including for testing).