Refactor window system

[mazkolain-zz]

Instead of using imaginary windows (views) use xbmc's own ones.

Using this scheme has the following advantages:

• Less memory usage (hopefully)
• Possibility to use window lists (which support inserts on every position of the list).
• Abbility to set list sorting (seems impossible with standalone lists).
• Modularized views (instead of a large unmaintainable xml file).

But sadly has some minor (and hopefully fixable) caveats:

• Figure out how to implement root windows that replace the entire window history.
• Must use includes for the main menu and common layout (should be easy with skinutils).
• No active content on common layout, as it gets replaced when navigating (scrolling text would probably hard reset and so on...).