Issue 145 - Add Variable Day of Month Option for DayOfMonthTrigger

[william-deeken]

This pull has the following updates:

1. Updating DayOfMonthTrigger to have a new data member "Date Type" with select choices "Variable Date" or "Specific Date".
2. The "Specific Date" selection would cause this trigger configuration to behave as is currently does. User has the ability to choose Trigger Days and Trigger Times.
3. The "Variable Date" choice will hide Trigger Days configuration and instead show "Nth Weekday", a value between 1-5 inclusive, and Weekday (Mon-Sun).
4. New methods DayOfMonthTrigger.GetVariableDateOfMonth, DayOfMonthTrigger.GetNextMonthWithValidVariableDate to handle getting the current month's next run time and the next valid runtime after the current month.
5. Update existing methods for new trigger type.
6. Resource files - Added new help text, dashboard schedule string format, for new settings/trigger type (English only).
7. Updated test project to test new functionality.
   I've attached a spreadsheet with all the test cases I came up with:
   VariableDate_TestCases.xlsx

[william-deeken]

Has there been any progress on reviewing this PR?