CI: No longer publish documentation PDF to Github

Since 'Github downloads' is no longer supported, this is rather useless.
CI: Disable Bitbucker <-> Github repository sync

Everything is moved to Github, so no sync is required any longer.
Move & adapt .hgignore to .gitignore
Rework version retrieval code from Hg to Git-compatible

This is partially based on the changes contained in
e2e8d007c743020a32314ca1a4487382f0556618
Add pattern matching 'git describe' output on Jenkins slaves
Add support for ARAKOON-347:Arakoon Logging Improvements