Reduce bundle size

[mjbvz]

This takes the ext bundle size from 20mb+ to 70kb. Main changes:

• Remove webpack as a dependency as AFAIK it is not used (and it should have been under dev deps)
• Remove vsce as a dep
• Remove the top level tasks and launch files as these should be under ./vscode instead
• Move images out of source into top level file (so that we can then exclude the entire src directory)
• Delete dist because this also seems unused
• Pass images through optimizer
• Remove extra copy of LICENSE under src
• Remove quickstart.md
• Remove yarn.lock since there's also a package.json

[kidonng]

@meganrogge Could you release a new version if you have time? This still taxes all current and future installations.