Make WMTS related errors be named consistently and correctly within open layers

[Schachte]

Description

We have been getting complaints about inconsistencies within our error messages, specifically referring to WMTS as WMT. This has caused confusion in our downstream projects as we refer to the same types of layers as WMTS elsewhere and WMT here.

This is a very small improvement to update these messages by making them read as "WMTS" instead of "WMT".

Example:

ddf/ui/packages/catalog-ui-search/src/main/webapp/js/controllers/ol.layerCollection.controller.js

Line 68 in 15f2049

throw new Error('WMT map layer source has no layers.')

https://en.wikipedia.org/wiki/Web_Map_Tile_Service

Expected behavior:

Have error messages read as WMTS in place of WMT.