refactor: rewrite proxy <=> client internals

[machour]

Description

As mentioned in #770, this is the smallest subset of changes required for the Proxy<=>Client refactoring.

• Client methods don't trigger the fetch() anymore, but instead hands out all call parameters to the Proxy
• only list and get operations are supported
• Got rid of the weird & confusing splitArgs() things.
• Our actions sets now contain the action "name"

Tested all the screens migrated to the new API so far, every one of them still work without changing a single char.

[coveralls]

Coverage increased (+0.3%) to 43.282% when pulling 911b561 on machour:refactor/proxy-client into 4b32a92 on gitpoint:master.

[housseindjirdeh]

Thank you so much for breaking things down into smaller digestable chunks :)

This looks great ✅