Cleanup and new commandline options to mkqt5bld script.

Removed commented code, removed commandline option build_webkit, added
new options:
- ignore=[module_name]  ignores the module
- silent_mode           add silent option for (n)make

make and make install is done for each module, not from the main
level.

Change-Id: I8a7a554e71c426cfc0831559da19ea0f74774efd
Reviewed-by: Simo Fält <simo.falt@digia.com>
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>