Channel Preferences Dialog: scan data source give info according to key, add data time

closes #98 (closed)

In Channel Preferences Dialog (CPD), when click Scan Channels from Data Source, data keys will be listed with radio buttons to select. Then channels displayed in Preferred SOH list and tracking box and the data time at the bottom are related to the selected data key.

If user open CPD without selecting a data set or the selected data set is RT130, the button 'Scan Channels from MSeed Data' will be disabled. User can add channels manually or get channels from DB.