Cleanup.
* Fixed preview issue when using an external Collection that does not contain Documents.
* Added `local-sort` attribute on columns definition to operate a JavaScript sort on that column.
* Added button in header of date columns to toggle relative dates display.
Merge pull request #310 from inthause/documents

Add new document Rbs_Catalog_Attribute
Added setting in user profile to define what to do when a Document is saved in an Editor ("back to list" or "stay on form").
Added directive on <time/> elements that allows display of relative dates.
Merge pull request #311 from fredericbonjour/Admin

Improvements in `<rbs-document-list/>`, User profile and dates display.
Price module US translation
Merge pull request #312 from franckstauffer/i18n

Price module US translation
[UPDATE] Refactoring in User and Plugins with rbs-document-list
Merge branch 'master' of github.com:RBSChange/Change into user
Merge pull request #313 from renaudJennyRBS/user

Refactoring in User and Plugins with rbs-document-list
[UPDATE] add HTTP Status 500 in error cases of Plugins Actions
Merge pull request #314 from renaudJennyRBS/plugins

[UPDATE] add HTTP Status 500 in error cases of Plugins Actions
UPDATE replace null by 0 for db document property