Reconsider including gutenberg.pot in the repository

[nylen]

In general a source control repository should not store files that are derived from other source files. With almost every code change we make, there are corresponding changes in gutenberg.pot. It's easy to miss updating this file (see #603 for an example), and I think we really only need it when we do a build. In that case, shouldn't we remove it from the repository (ignore it) and just cause it to be generated as part of the build step?

One thing that's not clear to me is where and how the actual translations of our strings will be stored, but I think this would be outside of source control as well.

[aduth]

This has become enough of a pain point that I'd agree it's probably best to ignore in the repository. Alternatively I'd considered having a bot to generate these automatically upon each commit, but there's not a good core reconciliation story there.

[nylen]

Changed this to a bug because earlier today it was the reason that #603 had merge conflicts with master. I fixed it on that PR, but still.