Win32 build system: Experimental bootstrap script

The goal of this script is to make is extremely easy to start gnucash
development on Windows. After downloading and running this script, the
user should be ready to start coding.

Note that this is not the case yet. The bootstrap script is only the
first step in that direction.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@22707 57a11ea4-9604-0410-9ed3-97b8803252fd