Added checksum field to database of checkables
 - Keep all configuration in the top level config file
 - Use the config item 'dataroot' to tell the d-i where to start
   checking
Make location of drill-instructor .db file configurable. Add a test
for specifying dataroot.
 - Look at the least recently checked item first
 - Suppress the hsi splash
 - Check one file in ten
Report what happens in the log file
 - Make the odds of checking a file configurable
 - If we already have a checksum for a file stored, fetch the file and
   compare it
 - Added a test for the issue where checksum was not being written to
   the database and fixed it
 - Better analysis of Checkable.check() returns.
 - Need to define Alert.py
 - Persistent drill-instructor statistics (probably need a way to
   reset these)