RestVerticle should check for implementation at startup

When RMBs RestVerticle starts, it checks for all interfaces in org.folio.rest.jaxrs.resource and makes appropriate paths and methods for routing. The check for actual implementation of the class is not performed until RMB gets a request. This has two problems:

1. Performance. Doesn't seem to be a problem but checking initially should be faster instead of doing it "per" request.

2. RMB throws an ugly exception for cases where a class is not implemented. This happens if the module is using a generated client. In that case, since the generated client includes the interface, it will throw those exceptions quite often.

While fixing this, it should also be possible to deal with RMB-319.