Add a WMTS CoverageReader

Description

This proposal aims to create a CoverageReader for remote WMTS layers, in the same way the WMSCoverageReader works on remote WMS layers.

When data are requested to the CoverageReader, the logic shall:

find the TileMatrixSet which does not need reprojection for the current request (if possible)
locate the proper tiles at the right zoomlevel
request the tiles to the remote WMTS,
mosaic the tiles

References:

A note about the authors: Implementation has initially been done by Ian Turton, and then continued by Emanuele Tajariol

The changes for this proposal are split on several modules:

ogc/net.opengis.wmtsv1: new module; contains the XML schema as defined in the XML GT documentation; includes the schema for GML311;
extension/xsd/xsd-wmts: new module; contains the XML bindings as defined in the XML GT documentation;
unsupported/wmts: new module; contains
- a human-friendly WMTSCapabilities model
- logic for tiles handling
- WMTS client (extends the TileService in the tile-client module),
- the CoverageReader.

No major changes have be made on the other modules, except for some compatibility issues:

extension/xsd/xsd-core: EMF dependency version has been bumped up (note that the artifactId has changed as well);
unsupported/tile-client: minor changes (private methods made protected to allow inheritance)

Choose one of:

Voting:

No API change needed for this proposal.

Since the WMTS cascading in GeoServer needs to be integrated into core modules, the dependant GT modules should not be unsupported.

Existing unsupported modules that needs to be moved are:

Note that the wmts module in the forked repo is under unsupported/ and should be moved out of there as well.