Adding Search endpoints and sqlalchemy impl

Search endpoints added for Projects, Stories, Tasks, Comments and Users.

SqlAlchemy plugin for fulltext search added.
The migration for full-text indexes added.
The migration checks the MySQL server version before creating indexes.

The default search engine via sqlalchemy added.

Change-Id: Ie3e4c4f317338d68e82c9c21652d49220c6e4a7d