Add setting to cap number of activity days to display

This patch adds a setting, 'web.activityDurationMaximum', that specifies the
maximum number of days of activity that may be requested. The default value is
30. When the number of days requested exceeds this value, the request is
handled as though the maximum value was requested.
Merge pull request #111 from atdt/master

Add setting to cap number of activity days to display