Implement a qmake-based build for Subsurface

This is working for me, but requires a bit more testing. To build,
run:
  qmake [options]

Where options might be:
  V=1               disable "silent" build
  LIBDCDEVEL=1      use side-by-side libdivecomputer
  INCLUDEPATH+=xxx  add -Ixxx (e.g., INCLUDEPATH+=/usr/local/marble/include)
  LIBS+=xxx         add xxx to the linker flags (e.g. LIBS+=-L/usr/local/marble/lib)
  or any other qmake option, including debug and release options

This new buildsystem does not look for libdivecomputer in
/usr/local. You must either pass LIBDCDEVEL=1 or libdivecomputer will
need to be found via pkg-config.

If your distribution is already using qtchooser in place of qmake, you
may need to pass an extra option to qmake to select the a
cross-build. For example:

  qmake -qt=i686-w64-mingw32-qt4

If your distribution is not yet using qtchooser, then you need to file
a bug report requesting it and you need to run the full path to qmake.

Note:
 - there are some ### left in the buildsystem
 - and version.h is generated at qmake time. It's not updated during make.

Signed-off-by: Thiago Macieira <thiago@macieira.org>