Fix slimerjs.bat that did not work anymore

Revert the pull request #63. Closes #84
Docs: add warning on the use of custom headers
Website: update FAQ
bumped stable version to 0.8.4pre
Backported the buildpackage script.

The 'nightly' parameter is not supported anymore
website: updated links to nightlies
Merge branch 'v0.8'

Conflicts:
	buildpackage.sh
	src/application.ini