Bug #5152 - "mouse double-click time is too low by default - 200ms"

We only use the doubleclick in one place in the default configuration,
for doubleclicking titlebars to maximize windows, so any negative impact
of increasing the timeout should be minimal, especially with the
addition of requiring the two clicks to be in the same place.

Doubleclicks are hardcoded to occur within 8 pixels for now, it doesn't
seem worth it to add a config until someone complains. A possibility is
using the drag threshold, but some people have that set very low so it
could be hard to doubleclick then.

Add the XInclude namespace in the default config file (named "xi")

Specify that it allows you to specify properties on the command line.
Update the variable names to _OB_APP_*.