Add starting plugin core, internal messaging port, and inspector JSON
Squashed commits:
[ba98299] clean things up
[d066c84] move inspector json out of views folder
[579f7cf] remove unnecessary comments
[e9d7c52] remove more react devtools stuff
[5c700b3] add inspector JSON and do some cleanup
[4abe686] remove react devtools
[b4cd4bc] get page context JSON and pass it to devpanel
[8b9c71b] add install instructions
[a8e30b7] log inspected page json route
[2331720] add blink devtools source as submodule
[c7c1a4b] reorganize similar to react devtools

clean things up

update readme (+1 squashed commit)
Squashed commits:
[e4b9e22] add skeleton code for devtools extension