Add explicit loiter direction field

[gillamkid]

Currently loiter direction can be changed from clockwise (default) to counterclockwise by making the radius a negative value, however this feature isn't very intuitive/discoverable for new users. It would be nice if there was an explicit field for loiter direction, similar to how Landing Pattern has its "loiter clockwise" field.

Current Loiter form inputs (note how there is no "Loiter clockwise" field)

Direction field in "Landing Pattern" form (notice how it has a "loiter clockwise" field. would like to have same field for "Loiter" waypoints)

[DonLakeFlyer]

Same problem here as I described in the other Landing Pattern issue. Loiter is a simple mission item and doesn't know much about the fields associated with it. Landing Pattern is a complex item which has its own custom ui for it. This is theoretically fixable but needs to be done in a generic way and would be quite non-trivial. Simple mission items as defined by json meta data. Would require plumbing some sort of negate it with a checkbox or something definition in the meta data which would be carried through from json all the way up to the ui. Doable, but a bunch of work.