Surround response language blocks with curly braces

[HeikoKlare]

We currently go without curly braces known from GPPLs in the response language since the end of a block is clear in our syntax due to the language design, except for Xtend code blocks.
For developers, it seems to be natural to have blocks enclosed with curly braces, as the range of a block can be recognized more quickly.

We should add curly braces to surround all blocks in the response language, e.g. match, effect etc.