GitHub adaptions

Minor fixes to stabilize the build and versioning after publishing on GitHub.

Changes:

• Build from GitHub provided tar and zip files now works (tests are not built in this case)
• gwhisper --version now gives useful output with builds from all tested build scenarios (i.e. Build from GIT repository, build from source archive and build as part of other repository)

First published version of gWhisper

NOTE: please do not download source code archives listed below, as they do not include the googletest submodule. Please clone the git repository.