Get rid of jQueryUI dialog for page preview and elements window.
Adds `Alchemy.Dialog` JS class and use this for all dialog windows.
Adds `Alchemy.ConfirmDialog` JS class and use this for confirm dialogs.

- Renames `Alchemy.openConfirmWindow ` -> `Alchemy.openConfirmDialog `
- Renames `link_to_confirmation_window ` helper -> `link_to_confirm_dialog `
Updates jquery-ui-rails gem and removes jQueryUI.Dialog \o/
Render proper message after clearing element clipboard.
Styling for forms getting displayed in main content.

If one opens a resource edit form in a new tab, it is now nicely formatted.
Uses function, instead of custom event as close dialog callback.

Fixes an issue with events sometimes not firing. Hey JavaScript events \o/
Adds a class to form of `button_with_confirm` helper.
Lots of layout fixes (sizes and padding of several dialogs, etc.).
Bump version to 3.0.0.rc3