Restrict polygon properties for avoid_polygons

[nilsnolde]

To prevent our servers from crashing, we should restrict some polygon property/properties a user can pass with avoid_polygon parameter. That should also go in the app.config of course.

Possible property restriction:

• area
• extent in X or Y, e.g. no more than 10 km in X OR Y

[takb]

@nilsnolde , 1. do we need both restrictions? 2. what are the values that endanger server stability?

[takb]

@nilsnolde it's implemented now and awaiting merge, but we need to have meaningful values to actually set.