Support for Real-time Mapping.

Add support for real-time mapping to AP2.
[Let's use this issue as one where we can create a number of sub issues to get to the final goal]

An example work flow is :-
- send back the pictures to APM Planner,
- stitch the images,
- create tiles and
- show on map,
while still flying.

To implement the above there are number of steps required

1) Implement auto-waypoint generation see #139
2) Auto download of Images see xxx
3) Image overlay see ???

The issue names no files, tests, or entry points. Start by reviewing the linked auto-waypoint work in #139 and breaking the remaining workflow into sub-issues for image download, stitching, tile creation, and map display. Done means the complete mapping workflow operates while the vehicle is still flying.

Written by the indexing model from the issue text.