Reorganise UF3P messages for 1.7 specific ones.

Adds new `common` entries for:
- `AlreadyInUF3Pmsg`: Container for the messages, to avoid repeating
  them for every UF3P version.
- `UF3Pfile_1_7`: Mods included in UF3P 1.7.
- `AlreadyInUF3P_1_7`: 1.7 specific version of `AlreadyInUF3P`.
Add data for `The Pitt - Fixes.esp`.

As supplied by @Kelmych - thanks!

Closes loot/fallout3#41.