Updates the README master branch note. [ci skip]
Removes accidentally included DummyApp tables from 2.6 migration file. Closes #431

Also removes the forcing of table creation.
Changes the way we check for existence of alchemy tables in migration.

We rejected the whole migration if only the alchemy_pages table exists. Now we check for every table first if it exists and then create it. This way the migration could be run a second time, if someone accidentally removed one of the tables.
Removes the shorten_to option from essence_richtext_view.
Validates for uniqueness of Content name in scope of element.
Refactors Admin::PagesController#copy_language_tree and its specs.

Removed unused code in context of layoutpages.
Converts link overlay form into new div based form layout.
Upgrades Dragonfly to 1.0.1
Updates Kaminari to 0.15.0
Updates Sassy-Buttons to 0.2.6
Fixes menubar scss mixins and adds new icon.
Removes unused ferret search lib.
Adds a complete callback for Alchemy windows.

The complete callback gets called after the window loaded its content.
Removes background image preloader jquery plugin.

It wasn't in use anyway.
Prevent default link event on element window's toolbar buttons.

Fixes an issue with Turbolinks always reloading the page while clicking on the element window's toolbar buttons.
Fixes Turbolinks issues with link overlay.
Removes unnecessary clipboard select helper and fixes select box css class.
Use stable compass-rails

compass-rails 1.1.x works with Rails 4 and 2.0.alpha.0 has been janked

See: https://github.com/Compass/compass-rails/commit/2c54193cdda7b152135a908c9481dca83f32045d
Set I18n.enforce_available_locales = true
Removes `render_essence_editor_by_type` helper.