Also includes general improvements to the slider widget such as an optional
"autotrim" function to cut off trailing zeroes, a "format" string that's easier
to internationalize, and general tidiness.
Previously we had no disk management whatsoever, so we cleared the cache on
every close just to prevent clogging up tester disk space. Now that we are
implementing disk management, there are better things to do on close regarding
disk cache. However, some users may still wish for the app to delete the cache
on close, so it's provided as an option.
itsmattkc