Support loadleveler job pre-empt/vacation

Handle `SIGUSR1` for loadleveler jobs with `restart=yes` directive.
On receiving a `SIGUSR1` signal, a job script will remove its status
file, and send a message to the suite to indicate that it has been
vacated. The server will reset the status of the task (job) to
`submitted`. This change resolve cylc/cylc#867.
Merge pull request #868 from matthewrmshin/handle-job-vacated-by-sigusr1

Support loadleveler job vacation: handle SIGUSR1
broadcast: allow overlapping inheritance

This allows broadcasts on families to be used with broadcasts on a task.
tests: remove unnecessary line in suite
cylc gui: remove hardcoded colours
cylc gui: remove commented out line
Merge pull request #883 from matthewrmshin/broadcast-inherit

broadcast: allow overlapping inheritance
Merge pull request #886 from benfitzpatrick/cylc.gui-change-colours

cylc gui: remove main window hardcoded colours