Revisit action names

Since their introduction, some actions expanded in scope, e.g. `get_file_metadata` handles more than a single file now. Maybe it is worth renaming them to account for this expanded scope (e.g. use `get_files_metadata`).

Additionally, some actions are OS-specific. It might also be a good idea to prefix (or postfix) them with OS name to make this clear. Or it might be not a good idea given e.g. `get_winreg_value` is obviously about Windows registry and thus is Windows-specific and such prefix would only introduce redundancy.

Also, originally the `get_*` and `list_*` prefixes were supposed to be indicative of whether the action returns a single or multiple results. This is not the case anymore and e.g. `get_file_metadata` can spawn multiple results even in case of a single path in the request. Perhaps these verbs should also be rethought.

This issue is more a remainder that some actions might be named suboptimally but it is rather low priority given more important problems to solve first.