Dinamically search for Qt tools (rcc/etc)

- Previously the call for rcc was hard coded in the Makefile. Instead we
  need to search for other options, rcc rcc4 rcc-qt4, just like we do
  for qmake and moc
- Instead of looking for all of the Qt binaries we should only search
  for qmake, and them query qmake for the location of the other
  binaries.
- Instead of using --with-qt-dir we not have --with-qt-qmake to point
  directly to the qmake binary