Implement directory monitoring using septag/dmon

Use a notification based directory monitoring based on the
septag/dmon lirbary instead of periodically rescan the whole
project's tree.

data/core/config.lua

@@ -1,6 +1,5 @@
 local config = {}
 
-config.project_scan_rate = 5
 config.fps = 60
 config.max_log_items = 80
 config.message_timeout = 5