Implement getTrustedRevision

[jglick]

See Javadoc. Should not be used with PRs on a public server until this is done.

[kmadel]

Currently PRs aren't supported at all - there is no API for Gogs yet to retrieve PRs.

[kmadel]

Will add getTrustedRevision support when PR support is added.

[sunmeplz]

Hi!
It will be awesome if you have a chance to merge some PR to master branch.
Thanks!