[modules][messages] mission: LLA waypoints in 1e7deg instead of float

A 32bit float has 23bits for the mantissa, which is a bit more than 7 digits.
Since you already use 3 digits to represent the part to the left of the decimal point, that leaves about 4 digits for the rest..
So in the worst case of 180deg you have a resolution of only ~3m!

With 1e7deg 32bit int you get ~1cm resolution.

addresses first part of #984