Fixed typos etc in setup script

Added also option to skip installation/removal of toolset and their
generation by the build script, if limited build to single Visual Studio
version.
Improved detection of PlayBook NDKs
Fixed a crash, when adding first NDK as 'custom'

Since it could happen no directories for NDK info caches created yet, data was
not saved correctly and an exception thrown later, at a time of selection not-known NDK.