Move editor and errorPane into a separate layout:

* error pane is now at the bottom of the screen under the tabs
* when error occurs, it should be more obvious and all of the error
  will be visible (no more needing to drag the bar across)
* error pane still auto-hides/shows
HTML escape errors (as the Qt client current use HTML to display them)

* Remove this in the future and put HTML escaping in client.
Set hard timing error buffer to be 0.5s + the sched ahead time:

* TODO: make this 0.5 user-configurable
* See what value works best on the RPi.
Fix spacing
Remove extra space with thread death error if thread is unnamed.
move current_bpm to default api file
Set max height for error pane to stop it taking up half the vertical real estate
wait for osc thread to complete before exiting.
move doc metadata after fn definitions
Improve formatting of error message
put RC name in ready message
rename start-server script to sonic-pi-server