Adds the gitlens icon to settings editor and welcome page

Updates dependencies

Replaces git content provider with git fs provider
Adds Buffer output support to git calls

Changes from out to dist
Adds size-plugin (commented out for now)
Adds image cache to improve bundle performance

Adds new webpack tree shaking plugin

Uses webpack for all of it

Consolidates ui dependencies & build into main

Fixes issue with new typescript
Pins node version to match vscode's version (7.9)