Bug 91881

Some issues concerning the GTK LaF support. I have attached a picture of NB
running under the GTK LaF and some theme. I have highlighted the problem zones. 
1. The first one is about the ugly icons used in the tab selector of the editor.
2. The second concerns the x and arrow used in the non editor tabs. They are
always black, they should change color with the theme. Also the shading (shadow)
of the
tab upper part does not always fit. The best would be if they would adapt to the
current form of the tab, but it may be easier to remove the shading completely
(although it's cool).
3. The third one is the color and the font style of the editor gutter. They
don't adapt to the theme or desktop settings (and to all unsupported LaFs?)
4. The font used in the editor status bar. It doesn't fits to the desktop
settings either.