Make preview icons and styles consistent

[juergmessmer]

The preview styles are refactored now and there for general use in all page types and plugins.
There are a few improvements that need to be done to make behaviour/styles consistent.

DefaultPageType:
• display edit (in preview bar) should be visible all the time (not only on hover) (see journal plugin)
• show filled_container:hover color also on edit button:hover (see journal plugin)

The styles should be the same for default page type preview and plugins and basic style included in preview-default.css, like new_entry button and menu f.e. in journal page type

JournalPageType:
• new_entry button (used in journal plugin) should show icon on hover too. Also it would be nice if it displayed correctly right from the beginning....?
• the menu should be styled too (consider general styles for menu, f.e. in admin-menu etc.