Add site name to translated strings and use instead of site name from db

[samuelsidler]

Currently, we input a site name when creating an O2 and when creating forums. However, it would be better if the site name was a string in the Rosetta project that was used instead of what was in the database. The site name is currently used in the sub-navigation and in the <title>, so we'll want to replace it in both places.

Ideally, we do this both for O2 and the forums at the same time, since they're both WordPress sites now. :)

[samuelsidler]

See #1951 as well.

[obenland]

@ocean90 Any idea when you might find time for this?

Or can you nudge me in the right direction here?

[obenland]

This is no longer necessary as it can be changed via the Customizer.