Enable standalone dependency on Qt

At some point in time we theorised that the solution to some
of our problems would be to also implement the lower (os_*)
bits of Vim. This could allows to do funky things like embedding
Vim and build solely against Qt. Here is a patch to get us started:

* We can build for UNIX, just with CMake - but ther is NO
  TERMINAL SUPPORT, just the GUI
* Currently this only builds on UNIX/Linux
* We still use the os specific header file, mostly for paths
* There is a lot of untested functions in os_qt.cpp
  ready to break
Assorted fixes to os_qt.cpp

* Add lots of debug calls
* Fix mch_FullName that always failed
* Fix mch_get/setperm
* Add mch_has_wildcards (from os_unix)
* Implement mch_expandpath
* Fix pathdef
* Add NO_CONSOLE define to disable terminal specific code
Add some forgotten code