Allow PhotoAlbum to be extended

Allow PhotoAlbum getCMSFields to be extended with DataExtensions
Add extension hooks

Add updateCMSFields hook to allow extensions to modify cmsfields
Add Thumbnailhook to allow extensions to return custom thumbnail
Pass Photos get method straight to Album

Perhaps I am missing something, but why replicate functionality from Album in PhotoGallery, when it can be called straight on the relating album?
Allow Photos method to be extended with extensions

If an extension to the PhotosAlbum class implements the GetItems method, this will be used instead of the default method
Changed GridFieldBulkUpload  setConfig to setUfSetup
Merge remote-tracking branch 'upstream/master'
Merge pull request #3 from guru-digital/master

Allow PhotoAlbum and PhotoItem to be extended. Allow custom thumbnail.