Refactor templates to language-specific directories

[Fleker]

Rename templates directory to work with pip namespace

Rebased work from #262

[Fleker]

This doesn't work as-is because resources cannot have subdirectories.

[polfeliu]

Don't know what problem you have with folders. I think I was able to do it in cantata: https://github.com/polfeliu/cantata/blob/8e4291407a9ac3ada48a380d0281cbcd327bc17e/cantata/main.py#L53

[Fleker]

Might be because you are pointing to the folder itself and not a file in a subdirectory.

[Fleker]

I'll merge this in now as the renaming will be useful ahead of a next release.