implement getting a route by uuid too

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | see travis
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

following the discussion with @ElectricMaxxx in https://github.com/ElectricMaxxx/CmfSeoBundle/pull/40 we noticed it would make sense to be able to look up routes by uuid too.