Bug 946678 - [Messaging] Creating a new message from contacts does not open the messaging composer when Messaging app is in background r=borja

Adds a hash for the "new" activity. This will have the side-effect of not
registering the notification and sms-received system message handlers which is a
good thing.
Merge pull request #14463 from julienw/946678-use-href-for-activity

Bug 946678 - [Messaging] Creating a new message from contacts does not o...