build improvements

Currently, there are two separate repositories for wkhtmltopdf and the patched QT. If we introduce the patched QT as a submodule, it is always possible to know which version of the patched QT was used for a given wkhtmltopdf build. Additionally, the static build scripts are simplified to a great extent as no checkout/clone is required (which improves build times).

A build script for MSVC 2010 and installer using NSIS have been added. The existing static build script needs to be reworked to not checkout the code and do the static build in the "static-build" folder, similar to the script for MSVC 2010 (which does an out-of-tree build in the above folder).

Going forward, we need to do the following:
* remove the WINE-specific part of static-build.sh
* simplify static-build.sh as mentioned above and rename to build_linux.sh
* add build_osx.sh for building of Mac OS X binaries