Replace gpac r4990 by gpac r5163

The gpac r4990 deb is no longer available for download, so use the
latest version instead. This is only a quick fix, a real solution would
involve not hardcoding a specific gpac version.
Merge pull request #145 from codecwatch/fix-pip

Fix library/REQUIREMENTS.txt
Merge pull request #146 from codecwatch/fix-deploy

Replace gpac r4990 by gpac r5163
Add credits
Set version of pytoolbox, because of v7