Add support for local use of the tiles (WMTSCapabilities.xml)

[sfkeller]

QTiles generates already local files directly (or packed into MBtiles).

When available locally, QGIS could read it directly as WMTS source if there is a WMTSCapabilities.xml file under directory "\1.0.0" which contains the correct path to this local file (OS dependent).

This WMTSCapabilities.xml could be generated by QTiles - in addition to the other options.

P.S. I've attached a working example of WMTSCapabilities.xml (See the 3 URI entries starting with "file:///C:/Daten/...". Works from zoom 0 to 21): WMTSCapabilities.xml.txt.