Add a 'warning' state for the notifications.

[xcoulon]

In Che, the notification manager can display messages in small, floating toasts on top of the editors or in the event bar at the bottom of the IDE. The NotificationManager is responsible for displaying these messages along with a status, defined by the org.eclipse.che.ide.api.notification.StatusNotification.Status enumeration.

In its current state, the enumeration provides with the following values:

• PROGRESS
• SUCCESS
• FAIL

Hélas, this does not fully match with the types of message defined in the Language Server Protocol where the types are:

• Error
• Warning
• Info
• Log

While it is possible to bind the Info and Log message types to the SUCCESS notification status, and the Error message type to the FAIL notification status, there remain a gap for the Warning message type.

This is issue is thus about adding a new value in the org.eclipse.che.ide.api.notification.StatusNotification.Status enumeration along with a triangle icon in the UI using the #F8E71C color.

Che version: 5.0.0-M7

Additional information:
Linked issue: #1793

[xcoulon]

Pull request submitted: #3113