rally: Support for rally landings.
mavproxy: Defaults for rally_breakalt and rally_flags
map: Line drawing to assist with Rally Landing mission planning.
param: Rally pointis lines redrawn upon update of appropriate params.
rally: "rally land abort" now accepts an optional altitude argument
map: ensure all objects have bounds() method

this fixes a rally display error
map: added a rallycircle setting

the circles can be a bit distracting!