Option to not allow logging time on Issues

[#1]

Description - Just as Timesheet Preferences can disallow logging time to Projects, add option for disallowing logging time to Issues

Why is this feature important to you - Only wish Projects and Tasks to have hours put to them

How would you like the feature to work - Add option in Preferences. Have overiride on Projects so that the Project Owner can decide whether hours can be logged on issues. Can be set on Templates in Issue Settings

Current Behaviour - Only Project Hours can be prevented