WIP: Upgrade/everything MJML APP v3

[iRyusa]

Lot of stuff to do still, react-icons major version update now export icons differently...

• Bump to Babel 7
• Bump to Webpack 4
• Update config to Webpack 4...
• Update to React 16
• Remove decorators from the project @connect
• Bump dependencies
• Update react-icons import (good luck with that : ) )
• Upgrade react-select to v3

Working on those issues:

• Keyboard Shortcut for Save #295 Keyboard Shortcut for Save
• Reorder projects, export and bulk open/upload. #300 Allow to add multiple projects, add maybe a order by last update ?
• Open Multiple Windows #297 Multi window MJML Project
• Tree style navigation with file icons #274 Add a file tree (might need some heavy rework here)

Maybe:

• Multi-tab Sublime Style #150 Add tabs ...

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Changelog

3.0.0-Alpha.1

• No feature, update all dependencies
• Perf improve, less ram consumed (mostly comes from improve in Electron nothing done in our side yet)

[iRyusa]

I'll move those in dev dep when finished