Add JSR305 as a dependency.

Guava uses these annotations, and the scala compiler prefers to be able to find them when it encounters them.
(Newer scala compilers behave better, but still emit warnings.)
Update to latest scala bug fix release.
Replace some code that uses commons-codec for base64 with the Guava equivalent.

The project doesn't currently depend on commons-codec, which was previously depended upon transitively.
Merge branch 'master' of github.com:RIPE-NCC/rpki-validator