[RFE] Create a way for the core and plugins to show notifications

[joaquimrocha]

Current situation

We may have functionality, both in the core and in plugins, that would like to inform the users about events that require their knowledge or attention, but the only code using it right now is the Edit/Delete/Apply buttons logic (cluster action).

Impact

No way of showing notifications that are not cluster actions.

Ideal future situation

We should have a more generic way of showing notifications. Like the clusterAction logic but generic for any needed notification.
Notifications should be of 3 kinds:

• Information: Blue snackbar
• Warning: Orange snackbar
• Error: Red snackbar

They should disappear after a while, and may have a button with a label + URL to link to.
They can also persist (not time out), but will need a close button in that case.

At a later point, each notification should be added to the notifications area we are planning in #19 .

**Implementation options

It should follow a very similar approach to the cluster action ones.
See this component.

Bonus points if the notifications result in a desktop notification when using the app.