Optional manual file-watching system

[handzlikchris]

File Watchers sometimes fails to trigger (likely system/Unity-implemntation issue) - better workaround would be FSR controlled watching system.

• To not affect performance badly we should only watch specific files

• easy approach could be to generate hash from file and re-check every N-seconds

• trigger reload and update hash if different

• there's already a functionality that'll allow to watch specific folders / files (that creates file watcher-setup entries and would play nicely to store that data)

• add option on file-watcher settings page to turn on with some explanation

[handzlikchris]

closed with #100