Extensive improvement of GTK2/3 consistency.

This is a fairly substantial overhaul of the GTK2 Mint-X theme to bring it much more into line with the look and feel of the GTK3 Mint-X theme. It matches colors and gradients between elements as closely as is possible.

It also includes:
    * cleaned up expander icons for the treeview
    * removes the pixmapping of GTK2 treeviews (which led to a dirty appearance which didn't work well in many applications)
    * adds a chrome.rc override file for a consistent chrome look.
    * GTK2 and 3 color schemes have been based on shades as much as possible, to allow the possibility of changing the entire theme's coloring from just the settings.ini and gtkrc.
    
Closes issue #12 and issue #13.

Sample of the new Chrome look:
![Sample of the new Chrome look](http://i.imgur.com/dBlyL.png)

Before changes (mint-themes currently):
[BEFORE](http://i.imgur.com/POUei.png)

After changes (this pull):
[AFTER](http://pbrd.co/TIHU0b)