Implemented TTMTasklistMetadata class to collect metadata on a task list. Also implemented tests for TTMTasklistMetadata class.
Added project, context, and priority count properties to TTMTaklistMetadata class.
Added modal sheet to display task list metadata. Keyboard shortcut: Command+I.
Merge branch 'feature/metadata' into develop
Changed the method by which alert sheets are called to add compatibility with OS X 10.8 (Mountain Lion). Closes Issue #34. Fixes the following functions for Mountain Lion: delete, postpone, set due date, set priority, append text.