Feature/update mapengine 2.0.x

[nesnoj]

Fixes #165

This

• updates to django-mapengine v2.0.1
• adds 2 WMS layers (temporarily using branch from Feature/custom sources and layers rl-institut/django-mapengine#20)

It basically works - can you have a quick look to see if the mapengine update is done properly and I did not miss anything? @henhuy

Also, I encoutered two problems:

1. The hover effect for the muns is not working anymore - it should look like this:
   
   However, the associated style region-line in layer_styles.json is used since when I change line-color or the default line width I see the change. Why not the hovering?
2. Having a WMS layer activated, I get errors in the console when zooming/moving around and could not find out why, maybe you can make more from the message. It does not seem to have any negative effect though.

raster_tile_source.ts:219 Uncaught (in promise) AbortError: signal is aborted without reason
    at $.<anonymous> (raster_tile_source.ts:219:34)
    at Generator.next (<anonymous>)
    at tslib.es6.js:121:71
    at new Promise (<anonymous>)
    at Object.e [as _] (tslib.es6.js:117:12)
    at $.abortTile (raster_tile_source.ts:218:13)
    at ct._abortTile (source_cache.ts:195:26)
    at ct._removeTile (source_cache.ts:867:18)
    at ct.update (source_cache.ts:656:22)
    at ce._updateSources (style.ts:1514:35)

[henhuy]

Fixed 1. issue
I already researched for a solution of second issue, but whether could find the reason nor a solution for it - already investigated an hour :(

[nesnoj]

Fixed 1. issue I already researched for a solution of second issue, but whether could find the reason nor a solution for it - already investigated an hour :(

Thx for fixing the hover! I wasn't ware that MAP_ENGINE_REGIONS is still needed in the new mapengine version.

Sorry for the complications on the 2nd thing :( . I also had a closer look (again), I thing it's sth about the bbox and CRS but let's leave it like this.

Last thing: layer order (z index), temp fix in rl-institut/django-mapengine#20 (comment)