Added key support for movie module

[nfearnley]

As of May 8, 2017, the OMDb API has gone private. From now on it requires a paid API key to function.
This change adds support for an api key in the configuration file.
It also changes the module command examples so that they will not fail the CI tests if there is no API key.

[dgw]

Typically, the modules included in Sopel core do not require API keys. The most likely outcome of OMDb's new key requirement is that movie.py will become part of sopel-extras, or become a separate project elsewhere.

[nfearnley]

I'll finishing cleaning up the code then, and setup a pull request to move it over to sopel-extras.

[dgw]

@nfearnley If you still have interest in working on this, I can now guarantee your PR will get looked at, whether you update this one (make sure to rebase on master and unignore the movie module from tests) or submit a PR to move the module into sopel-extras.

[nfearnley]

Thanks. I'll take a look when I can.

[dgw]

There's some overlap with #1195, I just noticed, which appears to switch providers altogether. Just a heads-up about potential duplication of effort.

[dgw]

Not going to merge this. Unless/Until we can find a keyless API for movie/TV data, the module's going to just disappear from core.