There was a bug in the web client creation and deletion of assetstores that failed to keep the collection of assetstores in a consistent state.
If we delete the current assetstore, make the most recently created assetstore the new current assetstore.
Added tests for assetstores.  For the webclient, added tests for creation, setting as current, and deletion of each type.  Added a test to the server to check that if the current assetstore is deleted, another assetstore is set as current.  Added some utility functions to help check if everything is loaded in the webclient.
Merge pull request #402 from girder/assetstore-collection-issue

Adding or deleting an Assetstore leaves the web client it an odd state.