Minor Russian translation fixes

[TheMysticSword]

Changes:

This PR fixes an issue with the Russian translation, where the "Map Music" menu in the Level Editor showed the string for Pushing Onwards as "1: Pushing Onwards (Потенциал для всего)" ("1: Pushing Onwards (Potential for Anything)"), and also adds Russian translations for song names when previewing their names in the "NEXT UNLOCK" dialogue with the Jukebox.

Legal Stuff:

By submitting this pull request, I confirm that...

• [x] My changes may be used in a future commercial release of VVVVVV
• [x] I will be credited in a CONTRIBUTORS file and the "GitHub Friends" section of the credits for all of said releases, but will NOT be compensated for these changes

[TerryCavanagh]

Thanks @TheMysticSword!