Add support for additional mw-nav compatible MSP way point types

[stronnag]

#The following MSP / mw-nav compat options are not currently implemented in inav. Please consider them for future releases. Maintaining MSP/mw-nav compatibility where practical is useful as it enables existing ground station software to be used. See https://github.com/iNavFlight/inav/wiki/MSP-Navigation-Messages summary follows:

• POSHOLD_TIME (P1 = time in seconds)
• SET_POI (lat, lon): craft always 'head in' to the SET_POI position
• JUMP - P1 = prior WP number, P2 = number of iterations (-1 until mission cancelled)
• SET_HEAD P1=heading (P1 = -1 cancels this mode and SET_POI mode)
• LAND (lat,lon,alt??)

RTH landing option is covered by #61

2020-04, strike out the 2.5 addtions.

[MichaelCWarren]

Is there any current plan to implement this in the near future?

[digitalentity]

That's a low priority at the moment. What types are you interested in?