[WIP] Page composer 

Add ability to 'compose' page block with a full ajax interface, providing template containers preview through configuration.

todo:
- [x] Fix inline javascript from block service
- [x] Save block positions on drop (jquery ui sortable)
- [x] Add ability to drop blocks on template preview
- [x] Add tests on Template Matrix Parser
- [x] Replace 'block list' link on page edit menu
- [ ] Add read-only option for template containers configuration 
- [x] Use ajax call to update blocks after edition
- [x] Add 'orphan' blocks
- [x] Fix unit tests ;)
- [ ] Add translations