views.dyn_images: create a image of flight paths

This uses the local mapproxy as cache for the background map.
Beware: this causes a dead-lock if you have only one single thread
for both the mapproxy and the frontend running.
model: add worldwide admin boundaries table
dyn_images: zoom to country's extent
dyn_images: choose a slightly larger overview
overview-table.jinja: add paragraph around content

Adds some space between the navpills and the content
dyn_images: gracefully fail if no mapscript available