Logging fixes

[DonLakeFlyer]

Problems fixed:

• Joystick code spitting out pile of this qgc.joystick.joysticksdl: Couldn't add GameController mapping: Couldn't parse GUID from # Game Controller DB for SDL in 2.0.16 format
• Joystick logging getting output even when not turned on
• PITA to turn off logging categories which are turned on and/or see which ones are on. Have to scroll through a big list

New logging dialog:

[DonLakeFlyer]

@HTRamsey I'm pretty sure the gamecontroller reading stuff is right. But you should check.

[HTRamsey]

I think there's an SDL command to read a whole file instead of line by line, but otherwise yeah that should be fine too