Do not let low-level expections leak through the API

[dlyash]

Currently, any RestMarketoClient's method may throw javax.ws.rs.ProcessingException or javax.ws.rs.WebApplicationException. Not only it exposes implementation details but also forces clients to deal with it on their own.

Proposed:

• Catch ProcessingException inside SDK and throw MarketoApiException instead
• the same for javax.ws.rs.WebApplicationException