Add new PublicationStatus document property constraint

Implement fromList attribute on Enum constraint
Merge pull request #254 from inthause/documents

Add new publicationStatus document property constraint
Refactor event registration.
Merge pull request #255 from inthause/documents

Refactor event registration.
Added possibility to execute code when a section is displayed for the first time in an Editor: implement `initSection(sectionName)` in your Editor's Scope, it will be called only once when the section is made visible.
Cleanup.
Changed default sort to be "modificationDate:desc" and fixed loading issues (especially when reloading the web page with sort parameters in the URL).
Added new `<div rbs-tip=""></div>` directive used to display a tip with "Dismiss" and "Dismiss forever" features (for now, the information is saved into the Local Storage).
Fixed default template for Document picker.
Cleanup.
Fixed error handling when the save process failed: display a message via NotificationCenter service.
Added properties name in the error message.
Fixed FunctionalPage::getPublicationSections() to return an array.
- Blocks can now declare their functions (setFunctions()).
- Added dynamic Collection of available Functions for FunctionalPage Documents.
Fixed navigation issues in Rbs_Website plugin.
Added FunctionalPage Documents.
Negative IDs are no longer sent when saving a new Document.
Section initialization (with initSection()) is now setup when the Editor is ready.
Properties popup in StructureEditor is now pinned by default.
Cleanup.