Move REST exceptions to common package

Allows their use in gutterball resources.
Add a friendly description for compliance event.
Merge pull request #705 from candlepin/dgoodwin/compliance-description

Add a friendly description for compliance event.
Fixed path issue for API lib.
Merge pull request #706 from candlepin/mstead/script-path-fix

Fixed path issue for API lib.
Merge pull request #704 from candlepin/wottop/gutterball-rest-exceptions

Move REST exceptions to common package