1307.11 - Group lead can slow down not working

[SchDerGrosse]

Bugs or user error on my part?

- Lead ship not slowing down allowing other ships to catch up regardless of the box "group lead can slow down" is toggled or not (see the Eisenhower CSG)

- Cannot group aircraft (see Swordswmen #8 and #9)

- Ignore plotted course not working on a group level (see F-15 at puerto rico, it is toggled to no, yet I have to go down to the level of the individual plane and set it to no manually)

[Geoffropi]

Logged, respectively :
#14973 (fixed)
#14972 (fixed)
#14974

[Geoffropi]

Fixed #14974 : this is due to forcing aircraft to be grouped with identical class.
it is now an option when grouping.