sbt model-view server prototype

This is a meta issue to track the progress of the sbt-server. Here, we'll try to outline all the TODO items to get to the first prototype release.

[x] Basic SocketServer handling multiple clients
[x] Initial single-queue-command-server-engine running requests.
[x] Fire started/finished/value task events
[x] Allow multiple clients to connect
[x] Capture stdout/stderr for users
[x] expose compatibility UIContext + plugin on the server.
[x] Capture TestEvents and fire down socket
[x] Capture compiler failure events.
[x] Return possible completions of strings
[x] Allow user to block for input or confirmation to the client running the most recent command request
[x] Revamp integration test suite
[x] Handle reload/set commands and BuildStructure change notifications.
[x] Key discovery mechanisms
[x] When listening to a TaskValue, also request it be executed.
[x] Fragment terminal into its own project that depends on the client lib.
[ ] Test on windows
[ ] Test on OSX

Optional tasks (necessary before actual release)

[ ] Use pure abstract API for serialization with bridges to play-json or whatever for now. #64
[ ] "In-Process" Client API exposed for play #64
[ ] Cancel Tasks being executed. Including cancelling queued commands.
[ ] Merge/Clear duplicate requests in queue..
[ ] Pull in scala pickles lib once compile-time-only option enabled.
[ ] Fix serialization registration for arbitrary value serialization. #64
[x] Document internal architecture
[x] Grab a ScopedKey by its string-form
[x] Add autocompletion/JLine to terminal client
[ ] Full set of tests.
[ ] Scala REPL workaround (autocomplete/input)

sbt / sbt-remote-control