New grid option for survey

I miss the option to program a simple grid of for example 10x10 meter. Mission Planner has already the option "distance between lines". But this works only for one direction (i call it X direction). Very nice would be if we have the same feature for the Y direction.

In the 1.3.35 version it's possible to get a grid of 10x10 Meter by adjusting the focal length and the distance between lines. With 1.3.38 the focal length do nothing, the grid won't be updated.

BTW, I use Win10

Reproduce the survey grid behavior in Mission Planner on Windows 10, comparing versions 1.3.35 and 1.3.38 with a 10x10 meter grid. Trace the existing "distance between lines" option and focal-length handling; done means the grid updates correctly and supports the requested spacing in both directions.

Written by the indexing model from the issue text.