CMSPage: Page toolbar
 - added a toolbar to the top of page.
 - added elements.less mixins.
 - small fixes to some other issues.
Updated .gitignore
CMSShared: Block Entity changes
 - blocks now directly have a cssClasses field. This'll change in the future.
CMSPage: Layout.js and LayoutCRUD changes.
 - added description field
CMSPage: CSS fix for scrollbars.
CMSPageJS: Fixes for block/layout rendering.
CMSPageBundle: BlockCRUD - added cssClasses field