Localize popup content

[AliyanH]

Localize the following for the popup, some of these localized strings are already available in options.js:

• "Focus Map"
• "Previous Feature"
• "Next Feature"
• "Focus Controls"

https://github.com/Maps4HTML/Web-Map-Custom-Element/blob/8370cace9bbc08a79fd28a15dc3a90f962dbef26/src/mapml/layers/MapMLLayer.js#L1255