Switch to Ubuntu.Components 1.2

[Stefano Verzegnassi]

All the Ubuntu phones are shipped with Ubuntu 15.04, so we can switch to the latest version of the toolkit.

QML imports should be updated as follow:

import QtQuick 2.4
import Ubuntu.Components 1.2

*** NOTES:
- "useDeprecatedToolbar" property of MainView is not anymore supported.

- ListIemWithAction from ./src/app/qml/upstreamComponents is no longer necessary. UITK1.2 ListItem should be used instead.

- Currently we are waiting for lp:~verzegnassi-stefano/ubuntu-docviewer-app/documentpage-add-contextual-actions to be merged.
  It includes a new TileBase component which drops the dependency on ListItemWithAction.
  However it provides a DocumentDelegateActions component in ./src/app/qml/documentPage, which may require further changes.
  Actions in the new ListItem are provided through a ListItemActions component, and it's something that should be kept in mind when updating the DocumentListDelegate or the DocumentGridDelegate component.
  Two possible solutions are:
       1) Change the list<Action> properties in DocumentDelegateActions to the ListItemActions type.
       2) Keep the list<Action> property type in DocumentDelegateActions, but use ListItemActions in DocumentListDelegate as appropriate.

[Ubuntu Phone Apps Jenkins Bot (ubuntu-phone-apps-jenkins-bot)]

Fix committed into lp:ubuntu-docviewer-app/reboot at revision 191, scheduled for release in ubuntu-docviewer-app, milestone Unknown