Consolidates to node-fetch 2.6.7 as Octokit requires v2

Reorganizes local git support to exclude from web
Swaps sha1 usages to md5 to avoid needing sha1 on the web (md5 is required by Gravatar)
Avoids crypto-browserfy and imports md5.js directly
Uses platform crypto for random nonce strings

Uses new quick pick buttons api

Removes gitlens.advanced.git setting

Removes unneeded typings file

appinsights seems to monkey patch even if explicitly disabled, so instead just only load it if needed

Also gracefully deals with the times when git isn't in the PATH