Add simplistic tile coverage scheme to account for tilt
Add simplistic tile coverage scheme to account for tilt

- fetches tiles of a single zoom level
- conservatively estimates coverage with an AABB of the view frustum projected onto the z = 0 plane
- limits tilt angle to prevent loading unholy multitudes of tiles at oblique angles

cleeus/tangram-es,xvilan/tangram-es,xvilan/tangram-es,karimnaaji/tangram-es,cleeus/tangram-es,hjanetzek/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,cleeus/tangram-es,cleeus/tangram-es,tangrams/tangram-es,hjanetzek/tangram-es,hjanetzek/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,cleeus/tangram-es,hjanetzek/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,quitejonny/tangram-es,karimnaaji/tangram-es,xvilan/tangram-es,tangrams/tangram-es,karimnaaji/tangram-es,karimnaaji/tangram-es,tangrams/tangram-es,quitejonny/tangram-es,xvilan/tangram-es,cleeus/tangram-es