Store all open dialogs in a collection for further reference. Refs #466

- Alchemy.currentDialog is now a function that returns the last dialog instantiated.
- Alchemy.closeCurrentDialog() now closes the last dialog instantiated.
Wait 'til the upload dialog is closed before refreshing the archive window. Closes #466
Styles the create language tree form. Closes #470
Fixes indention of haml element editor partial. Closes #472
Ensures that the redirect gets called even if no dialog is open. Closes #473
Removes duplicate please wait overlay call while saving page order.
Explicitly set the language_code after creating a page. Closes #474
Adds global help window accessible via ? key.

This help window only shows keyboard shortcuts at the moment.
Do not raise errors for element definitions having nil as contents value.
Fixes element partial generator for elements only having available contents.
Make url field for internal link editable.

So one could add a anchor manually.
Fixes add content button.
Fixes dynamic cell tabs creation.
Do not show help window if ? key is pressed inside of text field or text area.
Update README.md

Fix typo.
Merge pull request #476 from ingilniero/master

Update README.md
Use only ID selector to speed up test
Merge pull request #477 from GeekOnCoffee/spec_fasterness

Use only ID selector to speed up test
Allow select2-rails v3.4 and up.
Fixes issue with essence validation for uniqueness.

Validating the uniqueness of an essence always leaded to a failing validation because the way of finding a duplicate was wrong: We did not consider that we also find the essence that is currently validated.