Update 'Add WMS Layer...' to 'Add WMTS/WMTS Layer...' (followup d1de07a2)
and finish german translation

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perl -0777 -i.bak -pe 's#<source>Add WMS Layer...(</source>\s+<translation)>#<source>Add WMS/WMTS Layer...$1 type="unfinished">#' i18n/qgis_*.ts
perl -i.bak -pe 's#<source>Add WMS Layer...</source>#<source>Add WMS/WMTS Layer...</source>#' i18n/qgis_*.ts