Add cop PercentQLiterals

Checks `%Q` vs `%q`, and allow configuration to decide
if `%q` should be used when possible or if `%Q` should
be used always.

For #835.
[Refactor] Move common logic from on_percent_literal to caller
Merge pull request #1205 from jonas054/835_percent_q_case_cop

Add cop PercentQLiterals