Added a block that works like a container of blocks
Resize children of container blocks at box organizer
Reload plugin at each request on development mode

Core plugins extensions was not reloaded (development mode) between requests.
This breaks plugins which depends on extensions.
Added tests to container block pugin
Better edit mode to container block
Fix javascript for container block edition and enable move left/right
Add plugin blocks in acceptable_blocks for boxes
Fix method extension of container block that return a list of blocks (profile and environment)
Functional tests for container block
Add svg for container block icons
Render the container block box at container view

Render container block box and do not override children boxes
makes drag and drop functional.

Also fix article block to not use direct box attribute
and use owner method instead.
Test block move for container children on box organizer
Fix css for container block
Merge branch 'ActionItem2738' into stable