git-gui: Move frequently used commands to the top of the context menu.

git-gui: Move frequently used commands to the top of the context menu.

"Stage/Unstage Hunk" is probably the most frequently used command of the
patch context menu *and* it is not available in some other form than
the context menu. Therefore, it should go to the top. "Less Context" and
"More Context" entries are also not easily available otherwise, and are
therefore, moved second. The other entries are available via key strokes
(Copy, Paste, Refresh) or rarly used (Font Size, Options) and can go last.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>