Add IS_RELEASE_VERSION boolean.

Allows us to check if we are in a final release version or a development
one.
Also added tests for the new functionality.
Do not allow the use of 'danger' flag in release.
Add changelog, closed issue #3224.
Merge remote-tracking branch 'ivan-github/feature/3224_code-in-release-builds' into develop
Merge remote-tracking branch 'kali/feature/traffic_rates' into develop
Workaround some openvpn issues
try to terminate already running openvpn instance