Separate trusted calls/getters from rest.

[clangenb]

I would like that the app-lib/stf part is touched as little as possible when we add our encointer stuff. This refactoring is the step related to the bigger refactoring in #35. Example for the trusted call below:

// in app-libs
enum TrustedCall {
      ...
      Encointer(EncointerTrustedCall)
}


impl TrustedCall {
     pub fn account(&self) -> AccountId {
          match self {
            ...
            Encointer(call) => call.acount()
        }
     }  
}

impl ExecuteCall for TrustedCall {
     pub fn execute(&self) -> AccountId {
          match self {
            ...
            Encointer(call) => call.execute()
        }
     } 

    pub fn get_storage_hashes_to_update(&self) -> AccountId {
          match self {
            ...
            Encointer(call) => call.get_storage_hashes_to_update()
        }
     }  
}

// in encointer/stf
enum EncointerTrustedCall{
      ...
      ceremonies_register_participant(...)
}


impl EncointerTrustedCall{
     pub fn account(&self) -> AccountId {
          match self {
            ...
            ceremonies_register_participant(...) => account,
        }
     }  
}

impl ExecuteCall for EncointerTrustedCall{
     pub fn execute(&self) -> AccountId {
          match self {
            ...
            ceremonies_register_participant(...) => // do stuff...
        }
     }  

    pub fn get_storage_hashes_to_update(&self) -> AccountId {
          match self {
            ...
             ceremonies_register_participant(...)  => // do stuff...
        }
     }  
}

The cool thing about this, is that for every encointer specific behaviour in stf, we only add exactly one line into the app-libs/stf crate, which makes upstream merges much easier.