NSIS updates

* Updated the NSIS installer:
- it shows the GPL now
- it uses solid compression
- it appends the git hash to the exe
* Updated the documentation regarding these changes
* Updated the old COPYING file with the current gpl-2.0.txt from GNU.org to fix some indentations.

I don't know why git does this, but it includes the oracle changes I made some time ago, which are merged already. Hopefully this won't cause a problem.