database changes and reporting updates (1.0.18 - 1.0.20)

1.0.18 (2013/09/28)
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- Dropped table `#__dnagifts_lnk_user_gifts` is not used and is replaced
by `#__dnagifts_testresults` which is more complete
- Removed the emailing code from the progress update cron and set the
cron to run every 5 minutes

1.0.19 (2013/09/29)
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- Updated the healthcheck cron to run every 5 minutes, but only if there
were new test records.
- Replaced the emailing code in the healthcheck cron
- Added an 'is_timing_on' field to the #__dnagifts_lnk_user_tests table
to track the question-timing setting at time of doing the test.
- Added the code to update the is_timing_on, question_count and browser
into on the lnk_user_test table

1.0.20 (2013/09/29)
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- Dropped the browser_info field and added the fields user_browswer and
user_platform instead
- Added the user browser and platform to the the report.
- Tweaked the dashboard graph