[ENH] Adds "visible" fields and according rules
[ENH] Fov and model views autorefresh on changes via websocket

Adds new Signal classes specific to dialogs and fields of views.
Replaces the old way of detecting and notifying changes in fov.
[FIX] Timers are now working with signals like other actions

Timers were stored in a global variable, they are now attributes of the model
which let them being shared across threads and signals firings.
The system relied on is_alive() function to recognize new threads/timers 
from old ones. It now relies on a boolean associated to each timer, which is 
set to False when the run() method terminates.

Fixes #5 #1
[ENH] Clicks on (canvas) grid items prints the item name

A small opening on interactions with the "canvas" using clicks.
[REF] Removed spaces and new lines for sake of readability
[ENH] Clicking on items now can fire actions 

This highlights the fact that circular rules are not well handled by the state
machine at this point.