refs #440 - Filters on Hourly & Billable reports

See #440.

- Better handling of filters.
- Specific forms for Billable Hours & Hourly reports.
- Only include time for specified date range.  Previously, entries for the week which includes from_date were included, but only entries up to to_date were included.  Now, only entries from from_date to to_date are included.
- Show the range of dates which each column summarizes.
- Reorganized report tests.