Isolate state errors on the client-side

[gideonthomas]

Our client-side code mirrors a number of aspects of the server code.

One instance of this is in our message handler's when we 'check the message type/name' and 'check that the client is in the right state'. These two checks should be separated since if one of them fails, the client gets a generic error message which makes it hard to decipher whether an incorrect message was received or if its in the wrong state.

To fix this, we should first check the message, and then in each specific message handler, check the state before doing anything. If it is in the wrong state, we should throw a 'state' error as opposed to a generic error.

[gideonthomas]

Instead of the above approach, since states are almost irrelevant in the per-file syncing case, client-side logging will be used to log errors.