automatically configure prosthesis logging (fixes #378)

This changeset automatically configures prosthesis logging, so prosthesis logs when run on a developer machine (via `make run`, which invokes `cfx run`) but doesn't log when run on a user machine (via installation of a package created by `cfx xpi`).

Primarily, it changes the function used to log B2G stdout from *dump()* to *console.log()*, which then handles the decision about whether or not to log. But the changeset makes several other changes along the way.

1. Unconditionally enables logging in the simulator actor, so its logging behaves consistently.
2. Removes extra info from prosthesis log messages, like filename and line number. I understand that these can be useful, but they're inconsistent with the messages generated by all other code that logs, including core B2G code, the debugger server (and its actors), and all the modules, including the core SDK modules as well as the main addon's modules. (If it's important to record this information for a particular message, we can still make it do so by using *Cu.reportError()* or the equivalent.)
3. Moves the logging from Simulator to RemoteSimulatorClient, as this seems more like an internal function of RemoteSimulatorClient.
4. Makes logging in adb.js be consistent with logging elsewhere.
5. Fixes a couple of minor style nits.
6. removes the unused *logStdout* request type.