Don't install unneeded msysgit stuff.

- Don't install unneeded components like the shell extension etc.
We use python2, make that obvious.
Automatic download for WindowsSDK and installation of Debugging tools.

- No auto installation for full SDK yet. Unfortunately silent installation
  support is very limited and brittle. As we don't strictly need it for
  the symbol server for now only the debug tools are installed.
Setup is now able to initialize local symbolstore.