Fix Filter vs. FilterSet naming
Use pluggable filters for land and zoning apps
Fetch mapentity from git (develop branch) instead of pypi for tests

So we can test the develop branch of Geotrek with travis without releasing
a new version of mapentity on pypi.
Merge pull request #1046 from makinacorpus/791_pluggable_filters

Use pluggable filters for land and zoning apps (fixes #791)