PluginRespirator: Add client-side API connectToOtherPlugin() for connecting to a plugin with the new plugin FCP stuff.
- Deprecate function getPluginTalker() because the new API was designed to replace that.
- The name was chosen to be "connect*()" instead of "get*()" because connecting is a more generic and widely used term for communication between software.
- The name was chosen to be "connectToOtherPlugin()" instead of "connectToPlugin()" due to semantics of the containing class: PluginRespirator is an object which is handed to a plugin which is loaded into the node to keep the plugin supplied with all stuff it needs. So connectToPlugin() would sound like the plugin which owns the respirator is connecting to itself.
- The function FCPServer.registerFCPPluginClient() which it will need is not present yet, so compiling will fail. Add a TODO of implementing it nervertheless to describe what it should do.
- The new unrelated imports are because someone forgot to organize the imports when adding JavaDoc to other functions.