Allow arbitrary DayTimeInterval's

Awesome library thank you so much!

Currently a library consumer is forced to use any of the intervals as specified in:

Heron.MudCalendar/Heron.MudCalendar/Enums/CalendarTimeInterval.cs

Lines 3 to 8 in 4f6e4f9

    
           public enum CalendarTimeInterval 
        
           { 
        
               Minutes15 = 15, 
        
               Minutes30 = 30, 
        
               Minutes60 = 60 
        
           }

For the project I am currently working on I would preferably have a custom interval of 3 hours.
Let me know if this is something I can pickup and what the preferred way would be to implement this.

Thanks!

It's difficult to change it to an arbitrary amount now as it would break backwards compatibility. However I will add some more options to the enum including an option for 3 hours.

Thank you @danheron! I appreciate it!

	public enum CalendarTimeInterval
	{
	Minutes15 = 15,
	Minutes30 = 30,
	Minutes60 = 60
	}