This commit adds support for setting home clicking on map.
It is shown as another action in the submenu when we click
over the map with an active vehicle online.

As per mavlink specs, this command must use AMSL altitude,
so we need to first query terrain altitude, and when received
send the command.

Several checks have been implemented, and in case terrain
altitude is not shown at the selected location a popup will
appear indicating there are no terrain data for the specified location

…ider setting

…aseclass:

in order to make ElevationMapProvider be able to be base class
of anything besides Airmap. referrer was hardcoded to the base
class

… in elevation map provider:

This is to be on the safe side in case we have something
in the qeue for downloading, and the responses are somehow
messed up if we change provider, in case we are basing the
parsing of the response on terrain provider settings.

Maybe it is all right and it can be done correctly or even it
is already fine, but until super sure of that this is safer

We needed to decuple here in 2 scenarios:

1 - on updateForCurrentView: when _fetchElevation true, we use retrieve
    the elevation map provider selected from settingsManager->flightMapSettings->
    elevationMapProvider()

2 - on startDownload: We need to check here if the set selected corresponds
    to a terrain map provider, in case the fetch terrain data box is ticked,
    so we don't download twice. It used to be hardcoded to airmap elevation
    string

…r providers:

- getAltitudesForCoordinates: we get the name of the provider from settings for making
  the query, so the QGeoTileSpec of the query uses whatever map provider is set on settings.

- _terrainDone: this is the response to what we did above. Here we get the string for the
  map provider from the QGeoTileSpec itself, this way we are sure we are handling it with the
  proper hash, corresponding to the proper elevation provider.

- _getTileHash: we use here the map provider string from settings. This is what is called when
  getAltitudesForCoordinates is called. So this way we make sure it uses the provider indicated
  in settings.

NOTE: there is still work to do to make all this TerrainQuery file provider agnostic, this only
addresses the parts where we were hardcoding the string Airmap Elevation.

We used to have in QGCMapTileSet::_networkReplyFinished() this
serializeFromAirMapJson hardcoded to the airmap elevation string.

Instead we added functions in urlFactory and map providers so we
can understand from the map provider hash if such map provider
needs its tiles to be serialized, and if so, we call the same
provider to perform such serialization.

This way the base MapProvider class returns by default that no
serialization is needed, and the method to serialize just returns
the same QByteArray ( we should never use this, it is just a sanity check )

Then in Airmap elevation map provider we override this, and we
implement our own serialization method, which calls the
TerrainTile method that was originally called from
QGCMapTileSet.

This way it is also more obvious when developing support for new
elevation map providers, as the relevant methods are contained
within the elevation map providers definition files

…ude srtm1 ardupilot terrain servers

We implement again a method on QGCMapUrlEngine,
mapProvider and overriden in AP ElevationMapProvider
to check if tiles received need to be unzipped, and
also a method to unzip them