Draggable guide-point w/ altitude display, update on altitude change + distance from operator

Guide-point:
- added altitude display to guide-point marker
- added distance-from-operator view
- guide-point can be repositioned by dragging like other waypoint markers
- dismiss guide-point on APM mode change
- adjust guide-point altitude by touching (short) guide-point marker
- changing altitude with a valid guide-point (while in guided mode) will change the altitude of the aircraft
![screenshot-guide-point](https://f.cloud.github.com/assets/4014433/1306152/9b4c01d8-31aa-11e3-8ade-e2408043fd28.png)