Make the Add template button not wrap to the next line

By default, MWTitleInputWidgets are now 30em wide, but this doesn't
work in the transclusion dialog where we want to put the "Add template"
button after an MWTitleInputWidget and have it not wrap to the next line.
So make the MWTitleInputWidget on the add template page 20em wide instead
(this is what they all were before the default was changed to 30em).

Change-Id: I2f33a87427657f4e27939c401436c4ce6441208c