Add support for English versions of text items

[jakubklimek]

• [x] Dataset title
• [x] Dataset description
• [x] Distribution title
• [x] Data service title
• [x] Keywords

Everything except keywords can be done by adding a second field (on the same row).

Keywords will be tricky. We could add a second row of keywords in English, however, we would not know which Czech keyword is which English keyword. Instead, we will need to be able to add, edit and remove "multilingual keyword" in a dialogue, which will record that the keyword object has a Czech and an English label. See this form and its source.

Also see https://github.com/opendata-mvcr/nkod/issues/2

[jakubklimek]

Druhá várka vylepšení formulářů směrem k DCAT-AP 2.0.0

[jakubklimek]

I would place the button on the same line as the text inputs and choose an appropriate icon for the button (also for the spatial coverage). This way it is unintuitive.