Added emulated time recording as well as wall clock time.
Fixed recording time for multiple software items per system. An
incorrect constraint on the database table meant that time was only
being recorded for a single software item per system.
Detect the "empty" driver so the time spent at the selection menu isn't
recorded (you'd get multiple entries for this due to the way options
leak when returning to the system selection menu).
Included schema migration code to update existing timer plugin
databases. Also replaced some unnecessary floating point code with
integer maths, added log messages, and made the plugin unload unload its
database access code during emulation.
Changed other plugins' use of paths with trailing slashes as this causes
stat to fail on Windows.
