Truncate very long titles

[lehitoskin]

The program will throw a contract error if the title of the file is too long, so truncate it at a certain point.

[IonoclastBrigham]

What contract is it violating?

[lehitoskin]

It violated the label-string? for label in frame%. (label-string? v) Returns #t if v is a string whose length is less than or equal to 200.

Everything else is probably fine. We don't need to do anything special for file names in the database or thumbnail names (I think). It's just the label can't be too long.