Subscribe to channels before path_open

[nampereira]

To avoid losing messages during migration, need to subscribe to channels before the module is running (i.e. before path_open is called by the module).

Todo after basic migration is implemented.

(Change request to IOWorker to start a new stream from moduleIO.attachIO() to moduleIO.setupChannelsFromModArgs() ?)

[nampereira]

Related to this, we should save messages sent by the module after delete request.