Limit frequency of repeat test on admin test editor

[mamans86]

Update the test editor so that admin can limit the number of test attempts. this pull request based on issue number #379

[teddyvn]

The function is matching with my demand. Thanks for your effort. But design has small issue. It make confused repeatable =0 with repeatable = 1.

[mamans86]

I think this is naming issue on database table. repeatable = 1 mean the test can be repeat 1 time. Repeatable = 0 mean no repeat, repeatable = -1 mean unlimited. Repeatable=2 to 127 mean the test can be repeat 2 to 127 Times. Fill free elaborate this pull request with your change. Thanks for the report

[nicolaasuni]

This will require a change in the DB as the current table field is designed as boolean. This feature must work with all supported DBs.