app_dial: Allow fractional seconds for dial timeouts.

app_dial: Allow fractional seconds for dial timeouts.

Even though Dial() internally uses milliseconds for its dial timeouts,
this capability has been mostly obscured from users as the argument is
only parsed as an integer, thus forcing the use of whole seconds for
timeouts.

Parse it as a decimal instead so that timeouts can now truly have
millisecond precision.

Resolves: #1487

UserNote: The answer and progress dial timeouts now have millisecond
precision, instead of having to be whole numbers.