fix tests for p5
Support UUID user ids and improve email as login.

When switching on the 'Use email address as login name' option in
the security control panel, automatically update PAS to use
lowercase login names and migrate the existing login names.

Add 'Use UUID user ids' option in security control panel.

Both are part of PLIP 13419.
Update version to 2.4.x.

There is already a 2.3.x branch for Plone 4.2 and 4.3.
Remove hardcoded column styling in control panel overview.
Add changelog entry.
Adapt tests to the plonetheme.classic removal in Plone 5.
Fix test email: msgid was sent, not translation.
Merge pull request #16 from plone/2.3.x

Fix test email: msgid was sent, not translation.
remove calendar control panel
Merge pull request #17 from plone/davisagli-remove-calendar-controlpanel

remove calendar control panel
Add a warning, if plone.app.event is available but timezone is not set.
fix test
merge master