Using certain fractional "hours per day" values causes time tracking to not work

JIRA supports fractional values for the "hours per day" setting, but only if it corresponds to a whole number of minutes.

Examples of good and bad values:

• 8h = 480 minutes is OK
• 8.25h = 495 minutes is OK
• 8.23h = 493.8 minutes is no good

The problem is that it's possible to configure a bad value in the Time Tracking configuration screen, and no error is shown.

If you then try to log work that takes more than 1d, you will be faced with an exception:

Ideally we should use a different time representation that doesn't have this problem (e.g. use 8h15m instead of 8.25h).

At the very least we need to improve the error handling around the hours per day setting in the administration screens.