Add support for map layers via WMTS

Feature request/idea

A lot of map layers are provided via WMTS. Both publicly open and those that require a licens - and are protected with username/password. Support for this is partly implemented in the android version (you could load one wmts layer in the android version of Locus maps, that is why I say partly). I would love to see this also implemented in the iPhone version.

My wish list would be.

1. Implement support for WMTS-layers, with support for user name and password.

2. Implement support for multiple WMTS-layers. A WMTS-xml can contain multiple layers one could choose from. As an example, I have a map where two layers are different basemap layers, one layer is a name layer and one layer features national parks, nature reserves and protected wildlife nature. A prefered usage is to be able to choose a baselayer, and then one or more additional layers such as the name and/or protected nature layer as well. I'm pretty sure there are more similar services out there that have the same structure.

The map service I provide is covering Sweden and is available as a web map service at https://kartor.gokartor.se/ and I keep getting users that ask for a good app where my maps can be supported. I hope Locus Map can be that solution ;-)