Create score from template yields A4 even if default page size for system is Letter

Ubuntu 14.04, GIT commit: 408c73d

When we saved the templates for the Beta, we were careful to manually remove the page size tags, so that new scores created from them would inherit the system defaults. This was lost when the templates were converter to MSCZ. I wasn't thrilled about remembering to do that every time we made a change anyhow, but I think we need a way to address this. Two different approaches come to mind:

1) We could implement a "save as template" command that suppresses the page size tag if the page size is the system default (so you can still create templates that force unusual page sizes). This seems like it might be useful to end users as well, especially we also made it set the default folder to Templates. But it does rely on us remembering to use this facility!

2) We could implement a special case for Letter and A4 when creating a score from template, such that if the size is either of these two in the template, we substitute the system page size in the new score. Kind of hacky, but simple and effective.