Bump to sbt-remote-control 930843fabf194ef7c6a4575b0eb471c4ac9c373d
Ignore unknown execution IDs and nest tasks in executions

We can get an unknown execution ID because right now
sbt server doesn't report active executions to newly
connected clients.

Tasks are logically inside executions, not a global list,
though the task IDs are globally unique.
Merge pull request #583 from typesafehub/wip/havocp-update-sbt-rc

Use latest sbt-rc and slightly clean up execution state tracking in JS