Switch api_rottentomatoes to use requests

Removes flexget.utils.urlopener and flexget.utils.json dependencies.
Appears to fix rottentomatoes api returning ids as either ints or
strings- all tests which were failing because of this now pass.
Changed test title in test_rottentomatoes

Dropped 'in' from 'Star Wars: Episode I - The Phantom Menace (in 3D)'
as parser was not able to strip this, causing rotten tomatoes to be
unable to find the movie. Test therefore now passes.

Maybe a relevant thing for parser testing, but the aim here is test
rt functionality rather than MovieParser so removed.