[scripts] rewrite qt and qtc build scripts

TODO: integrate windows qt build to the same script

qtc build script works in msys git bash, if additionally
7z is found from the PATH.

http://code.google.com/p/msysgit/

Signed-off-by: Juha Kallioinen <juha.kallioinen@jolla.com>
Merge pull request #2 from sailfish-sdk/kalts-wip

[scripts] rewrite qt and qtc build scripts