Make EmailActivity the default activity.

We still go through Welcome when the app is launched from account/mailbox
shortcuts or a widget, to clear all existing activity instances, but
when the app is launched from the launcher we just open EmailActivity.

This will get rid of the flicker.

Change-Id: I9bff31fb96e24c125ddc0a1e30a007e6d6ff036d
1 file changed