update of version and changelog
Merge branch 'release/2-0-1' into release/3.0
Bump version to 3.0.8

Due to our (new) convention plugins inherit their versions from the
OpenProject core. The next stable release of the OpenProject core is
3.0.8.
Update of dependencies due to new versioning convention
Merge branch 'release/3.0' into dev
Bump version to corresponding core version