Get origin and resolutions from GetCapabilities for WMTS

[dafvid]

We're using QGIS-Server and the TileMatrix resolutions and origin is a per project setting. So it's not uncommon to have different settings for each project and for each WMTS-service. However, even though PR #236 added an option to have different origin and resolutions setting for each source, it's still a hazzle to have to dig out origin and convert scale to resolution for each service or to edit all projects to have the same tilegrid.

Describe the solution you'd like
I'd like for Origo to read the origin and tilematrix setting directly by parsing a getcapabilities document.

Describe alternatives you've considered
The alternative now is to use FME to create a sample source config. Also if I ever change the extent och tilematrix of the project it will misalign in the map.

Additional context
The resolutions are calculated from ScaleDenominator*0.00028 for each TileMatrix
The origin is extracted from TopLeftCorner for each TileMatrix