When starting HiTL, GCS set the home location, but did not identify it
as set=true. This patch fixes the behavior, as well as a minor variable
change to improve clarity.
Introduced new UAVOs in preparation for path planning refactor.
Changed STANDARD_AIR_SEA_LEVEL_PRESSURE from KPa to Pa.
Removed fixed-wing settings aimed specifically at CC. This was no longer
necessary.
Added MIN, MAX, and sign macros to misc_math.h. The sign macro returns -1
for values less than 0, and 1 for values greater than or equal to 0. 0 is
specifically not handled different from strictly positive numbers.
Added path manager module. The path manager's function in the navigation
hierarchy is to pass the appropriate path segment to the path follower, and
monitor the path follower's progress.

Several new functions were introduced into misc_math. These functions
calculate certain geometries which are useful for dubins paths.

Lastly, three sample paths were provided. 1) A return home, 2) a position
hold, and 3) an example path that can be used as a base for further
path programming.
Removed path planning elements from manualcontrol.c.
Refactored path planner. The path planner's role in navigation is to take
user-defined waypoints and provide a path that connects them together.

The path planner is supplied with two algorithms, "direct" and "direct-
with-filleting".

"Direct" goes directly to the waypoint, no matter how severe the
angle between two consecutive waypoints.

"Direct-with-filleting" adds fillets
to the direction changes, in order to provide smoother, more realistic
paths for dubins cart vehicle classes, i.e. vehicles that have a minimum
turn radius.
Refactored fixed-wing path follower to use math from known good version.
Updated makefile to support new navigation chain. An option was provided to
easily disable the path planner.