[#1178] Send email to the invited user

I removed the time.sleep(0.1) on TestMailer. Looking through the code, I
couldn't find anywhere where a timer looked needed. And I ran these tests a
hundred times without the timer to see if I could make them fail, but no. So, I
guess they're not needed anymore.

I also had to move the RESET_LINK_MESSAGE inside get_reset_link_body(). This
was because, when importing ckan.lib.mailer in ckan.logic.action.create.py, I
got:

    TypeError: No object (name: translator) has been registered for this thread

This seems to be because we were using _() before pylons had a change to set up
the translator. Moving it inside the method solves this.