Add flow control to protocol

[floesche]

A (much) later version of the protocol might want to use flow control. For example, if a type or plugin has a store_as value, the implementation would store the return value from the function or plugin as that value. Let's say the flyris plugin has a get_mm method, we could use that the following way:

block:
    conditions:
        - id: "active_background"
          commands:
            - plugins: "flyris"
            - method: "get_mm"
            - store_as: "open_width"
        - type: "if"
          variable: "open_width"
          condition: "> 50"
          then:
            - plugins: "flyris"
              method: "open_mm"
              params:
                  width: "30mm"
          else
            - plugins: "flyris"
              method: "open_mm"
              params:
                  width: "30mm"

Switch statements etc could be implemented in a similar way.