Adds preview action runner extensibility api

Adds button to rebase editor to toggle it on/off
Adds commands to toggle rebase editor on/off
Adds settings UI to toggle rebase editor on/off

Moves avatar cache to global storage
Improves avatar cache updates/resets
Improves contributor avatar fetch update

Renamed to Gutter Changes
Provides local changes if any, or recent commit changes
Distinguishes between added, changed, and removed lines
Shows a hover for the full diff hunk
Shows diff even with unsaved changes

Changes heatmap colorization for better clarity
Changes blame avatars to be w/ the annotations rather than in the gutter

Adds setViewsLayout command

Giving up on better else/catch/finally formatting -- can't fight anymore
Switching to tabs for better accessibility
https://twitter.com/sh4na/status/1146837957200027648

Splits App into AppBase & AppWithConfigBase for impl of new webviews

Adds bundle analyzer
Adds circular deps analyzer
Switches to es2018 output
Removes many circular dependencies

Keeps all path manipulation on the host rather than guest
Fixes shared/local path munging for mac/windows
Keeps current user lookup local when a guest
Keeps difftool lookup local when a guest
Avoids fetch date lookup when a guest
Stops clearing node_modules (for now)

Updates README (wip)
Updates welcome & settings pages (wip)

Adds ability to start a compare directly from the view

Renames showCommitInResults to showCommitInView
Renames showFileHistoryInResults to showFileHistoryInView

Changes changelog image links to permalinks
Moves all images for docs into a docs folder
Removes unused images

Closes #354 - Adds line history explorer (wip)
Closes #456 - Adds repository status to the repository nodes

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

Adds menu & toolbar settings to the settings editor
Adds mode setting for settings editor
Adds sticky header to settings editor