[REVIEW ONLY] Landing livedev2 in Brackets

[sebaslv]

This is just an initial commit for moving livedev2 extension to Brackets core as per in njx/brackets-livedev2#24. Current implementation was moved to LiveDevelopment/impls/default. livedev2 implementation was added to LiveDevelopment/impls/livedev2

They can be switched by a preference named: livedev.impl which is being checked at LiveDevelopment/main.js.

@busykai, please review this initial commit to validate overall approach and PreferencesManager usage. It seems that is not retrieving pref value when manually setting it at project level in .brackets.json

[busykai]

@sebaslv i see browser launcher being added as part of it. it wasn't part of the original repo. are you adding a fork of livedev2? we need to add vanilla livedev2 in its current state.

EDIT: the entire contents of transports/node/node_modules of livedev2 seems to be bring a lot of extra code compared to njx/livedev2-brackets

[sebaslv]

closed in favor of #2