Geo Location component (#15953)

* initial working version of a geo location component and georss platform

* ensure that custom attributes don't override built-in ones

* bugfixes and tests

* fixing tests because of introduction of new component using same fixture

* improving test cases

* removing potentially unavailable attribute from debug message output

* completing test suite

* cleaning up debug messages; sorting entries in group view by distance

* ability to define the desired state attribute and corresponding unit of measurement; sort devices in group by configured state; find centroid for map if event is defined by polygon; updated tests

* sort entries in group; code clean-ups

* fixing indentation

* added requirements of new component and platform

* fixed various lint issues

* fixed more lint issues

* introducing demo geo location platform; refactored geo location component and geo rss platform to fit

* removing geo rss events platform; added unit tests for geo location platform and demo platform

* reverting change in debug message for feedreader to avoid confusion with new geo location component

* updated requirements after removing georss platform

* removed unused imports

* fixing a lint issue and a test case

* simplifying component code; moving code into demo platform; fixing tests

* removed grouping from demo platform; small refactorings

* automating the entity id generation (the use of an entity namespace achieves the same thing)

* undoing changes made for the georss platform

* simplified test cases

* small tweaks to test case

* rounding all state attribute values

* fixing lint; removing distance from state attributes

* fixed test

* renamed add_devices to add_entities; tweaked test to gain more control over the timed update in the demo platform

* reusing utcnow variable instead of patched method

* fixed test by avoiding to make assumptions about order of list of entity ids

* adding test for the geo location event class