[#7257] ticket:562 Introduced base class for indexable objects
[#7257] ticket:562 Added proper index methods to Project model
[#7257] ticket:562 Added tests for 'add_project' index task
ticket:562 Added session extension for indexed objects
[#7257] ticket:562 Made indexer extension work with multiple models
[#7257] ticket:562 Made extension log exceptions and fail silently
[#7257] ticket:562 Fixed tests
[#7257] ticket:562 Fixed tests
[#7257] ticket:562 Added 'created' field to project's index method
[#7257] ticket:562 Fixed docstrings & refactored index tasks
[#7257] ticket:562 Fixed index tests
[#7257] ticket:562 Changed solr fields for Project model
[#7257] ticket:562 Fixed index tests for Project
[#7257] ticket:563 Add ScriptTask to (re)index all projects
[#7257] no need to delete doc (solr overwrites by id)
[#7257] handle error case on deleted project
[#7257] update fields indexed in solr for projects

* category_id is very old and not used
* use ProjectRegistrationProvider to get project create/register time
* add flags for nbhd proj, and root (aka not subproject)
* add external homepage
* do exact match on project and nbhd names
[#7257] factor up the common index_id method
[#7257] ticket:587 Get rid of unnecessary add_projects tasks
[#7257] ticket:587 Add unit tests