/sync diff command.

[cburschka]

While it is impossible to merge settings (and probably will always be, because 3-way merging requires tracking config changes, and eventually we have a reimplementation of git inside the settings manager of a small chat client), it should be possible to show all the different values side by side.

Eg

Differences between local and remote settings:

debug
   Local: 1
   Remote: 0
textColor
   Local: #ff0000
   Remote: #ffff00
notifications.sound.receive
   Local: null
   Remote: sound_1

This will then allow users to decide whether to pull or push settings, and maybe manually change the other settings.