Description of problem:
When attempting to use the rest api via a browser (which sends in the header a type of text/html) an error 500 is returned. It would be more appropriate if the error indicated "incorrect mime type" or similar.

Version-Release number of selected component (if applicable):
3.2.0

How reproducible:
Easy always

Steps to Reproduce:
1. Navigate a browser to https://translate.zanata.org/zanata/rest/projects
2. Note the error 500
3. In a console enter 
 > curl https://translate.zanata.org/zanata/rest/projects
4. Note the successful xml list

Actual results:
On entering the url into a browser, an error "500 Error processing Request" is displayed, and logging shows
> Failed to process REST request: java.lang.IllegalArgumentException: Failure parsing MediaType string: text/html,application/xhtml+xml,application/xml

Expected results:
Something a bit more user friendly.

Additional info: