Fix BL-758 Make a way to remember window size

By default, we still want to just maximize each time. But Susanna,
who is doing videos, needs a way for Bloom to go to the same size
each time. With this PR, there is a new setting in user.config,
"MaximizeWindow". To enable this new feature, "MaximizeWindow" must be
set to "False" in a text editor. After that, the window size and
location will be remembered, using an existing class from libpalaso.
Be nice if there was some way to tell whether the old settings already had this property, so we don't reset it if the user purposely made it false. Maybe we could check the old version number? But probably not worth bothering as long as this is primarily just for one person.