Consider reorganizing the parameter structure

[pasqu4le]

Clarification and motivation

Currently the contract parameter is a "flat" structure, meaning that in Haskell code it is a single datatype with several fields for entrypoints (that don't have their own entrypoints within).

This was done like this mainly because there are shortcomings in the produced documentation otherwise, see [morley/#768](TM-466 check and discuss mirroring failures).

It would however be better to split it into sub-parameters, so that:

1. entrypoints with different "scopes" would be separate
2. entrypoints that have common initial instructions (e.g. a check, see here) can be grouped to reduce duplication

so, we should consider switching to this.

Acceptance criteria

1. The parameter is split in multiple sub-parameters for efficiency and clarity.
2. Documentation generation is either fixed upstream or a workaround is used.