gedit: add css for document-panel drag'n drop part
headerbar: match pixel height for image buttons

- chasing the single pixel difference. of couse solving
  this with padding is a little futile in that the font
  size will break it.

  https://bugzilla.gnome.org/show_bug.cgi?id=721622
osd toolbar: flat and subtle backdrop

https://bugzilla.gnome.org/show_bug.cgi?id=725748
Fix dark pixels in outer top corners of leftmost and rightmost linked buttons

https://bugzilla.gnome.org/show_bug.cgi?id=704735
Add inode-directory-symbolic.svg

This file is a symlink to folder-symbolic.svg.

GLib uses 'inode/directory' for folder mime types. Adding this symlink
here so that it can stop special-casing folder icons.

https://bugzilla.gnome.org/show_bug.cgi?id=726046
Revert "Add inode-directory-symbolic.svg"

This belongs to gnome-icon-theme-symbolic, not sure how it got here.

This reverts commit a44b6dba610943113d448b85804350054815ce08.
prepare for 3.11.92 release
3.12.0
Bump version