Added DMM Trailer

[seeyabye]

This PR adds a DMM trailer for DmmJA.

[seeyabye]

I realized that there's different trailer qualities. I should check this accordingly.

[jvlflame]

Thanks for the PR @seeyabye!

For reference on the R18 scraper, I just have it default to the highest quality version rather than output all found qualities.
Have you tested the function on both the English/Japanese dmm sites, or only the Japanese one?

[seeyabye]

I have revised the way of getting the trailer URL. It should now get the highest quality by default as well.

As for the tests, I've only done it on the Japanese DMM site. I'm not too sure how to test it on the English DMM site as I constantly get redirected back to the Japanese version.

[seeyabye]

I've incorporated the fix. @jvlflame do you mind checking if it works for dmm? Thanks!

[jvlflame]

After further testing, turns out we do need to incorporate the websession in in $trailerPageUrl.
I made a few small changes to resolve that, so we should be good to merge.