Support for AJAX in minisites content + fixes

• Added aliases creation in DB for all assets to support direct links to aliased assets:
  • Added filesize and filemime fields for assets table.
  • Added update hook to update schema
  • Added update hook to update existing minisite instances using batch + archive fetching.
• Fixed assets not being deleted correctly when removed from the node form + test.
• Added returning of cache headers when accessing asset.
• Removed support for entity revisions as it was not implemented correctly.
• Added tests for Minisite class.