So far contains just a button to start the mailmerge wizard, and it is shown
when the mailmerge wizard starts.

The plan is that the last 3 steps (Edit document; Personalize document; Save,
print or send) will be removed from the wizard, and instead introduced in the
mailmerge toolbar.

Change-Id: I3a55a5b3b8a73bc6775579ac42c4ae30c6c9bac6