GPII-752: Add status messages to allow the user to know what's happening in the system

This pull requests adds status messages for:
 - Saving and thus logging in (PMT)
 - Loggint out in PMT
 - Saving and Applying in PCP
 - Making a change in the settings in PCP
 - Logging out from PCP

Currently, with this pull request the whole workflow of PMT & PCP is being described with short status messages.

It was decided in the comments of http://issues.gpii.net/browse/GPII-752 that the status messages will move along, in parallel with the functionality of both panels. Once another functionality part is added, the issue perhaps should be reopened to reflect the functionality improvement with another message.
@jobara the reason `modelListener` hasn't been used is mentioned here https://github.com/GPII/prefsEditors/commit/be2e971860a9e807201342cccc80241866c404d2. This way "Preferences modified" will be shown on load, that's what I've tried to avoid.

About the order of the events being fired, when I put the onLogout listener in the `fluid.prefs.GPIIEditor` component (and removed it from prefsEditor comps of course), pressing "log out" fired 1) onSettingChanged 2) onLogout 3) onSettingChanged 4) onLogout 5) onSettingChanged. In the current state of the listeners, logging out fires 1) onSCh 2) onSCh 3) onL 4) onSCh 5) onL, that's why the final message is correct.

Why are so many events being fired anyway?