v1.4.0 Add tray bar icon

Added

• add tray bar icon that changes according to state of tasks (green
  if at least one task is idle, red-yellow-green if all tasks are
  idle); please note that Java currently reports the wrong icon size
  for i3bar

• show current task states in tray bar menu

• allow users to disable tray bar icon

• check status of watches in parallel threads

• clean up when application ends

Changed

• breaking changes (please see README):

  • rename task states to improve code readability

  • read settings from EDN file

  • change section "scheduler" in configuration file to "settings"

• correctly licence files

• update documentation