git-gui: Use more modern looking icons in the tree browser

This is a replacement of all of the icons in our tree browser
window, as the prior icons just looked too 1980s Tk-ish.  The
icons used here are actually from a KDE themed look, so they
might actually be familiar to some users of git-gui.

Aside from using more modern looking icons we now have a special
icon for executable blobs, to make them stand out from the normal
non-executable blobs.  We also denote symlinks now with a different
icon, so they stand out from the other types of objects in the tree.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -1296,32 +1296,6 @@ static unsigned char file_merge_bits[] = {
    0xfa, 0x17, 0x02, 0x10, 0xfe, 0x1f};
 } -maskdata $filemask
 
-set file_dir_data {
-#define file_width 18
-#define file_height 18
-static unsigned char file_bits[] = {
-  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xf8, 0x03, 0x00,
-  0x0c, 0x03, 0x00, 0x04, 0xfe, 0x00, 0x06, 0x80, 0x00, 0xff, 0x9f, 0x00,
-  0x03, 0x98, 0x00, 0x02, 0x90, 0x00, 0x06, 0xb0, 0x00, 0x04, 0xa0, 0x00,
-  0x0c, 0xe0, 0x00, 0x08, 0xc0, 0x00, 0xf8, 0xff, 0x00, 0x00, 0x00, 0x00,
-  0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
-}
-image create bitmap file_dir -background white -foreground blue \
-	-data $file_dir_data -maskdata $file_dir_data
-unset file_dir_data
-
-set file_uplevel_data {
-#define up_width 15
-#define up_height 15
-static unsigned char up_bits[] = {
-  0x80, 0x00, 0xc0, 0x01, 0xe0, 0x03, 0xf0, 0x07, 0xf8, 0x0f, 0xfc, 0x1f,
-  0xfe, 0x3f, 0xc0, 0x01, 0xc0, 0x01, 0xc0, 0x01, 0xc0, 0x01, 0xc0, 0x01,
-  0xc0, 0x01, 0xc0, 0x01, 0x00, 0x00};
-}
-image create bitmap file_uplevel -background white -foreground red \
-	-data $file_uplevel_data -maskdata $file_uplevel_data
-unset file_uplevel_data
-
 set ui_index .vpane.files.index.list
 set ui_workdir .vpane.files.workdir.list