Use new possibilies to respect context with DeepL

https://developers.deepl.com/docs/v/de/api-reference/translate

states, that context is only respected, if you transfer multiple sentences within one text unit.

Therefore the possibilities to use context that DeepL now offers should be used.

We should transmit multiple sentences within one text unit to DeepL and use markup as explained here:

https://developers.deepl.com/docs/v/de/xml-and-html-handling/structured-content

We should not use the new alpha-version context attribute as this seems to be intended for context, that should not be translated.