compile with gtk3

Most changes are copied from mutter 3.4.0. So thanks to mutter
developers! They done all hard work.

Mostly I copied only things that was required to build metacity
with gtk3, but this commit also includes other changes:
1) Applied one patch from ubuntu (06_Add_UXD_shadows_and_borders.patch).
2) Renamed libmetacity-private to libmetacity-private3.
3) Changed metacity version to 3.10.0.
4) Removed many functions that was not used by metacity.