Alter DB structure, add output method, ordinal

Add user attempt serial number (ordinal)
Change exception type on file transfer error

Now throwing moodle_exception instead of regular Exception
Add outputmethod and error language values
Simplify code, add field check

What field is shown is now controlled by task settings.
Page shows main (grading attempt) and then other attempts.
Main attempt is chosen based on task settings.
Bug fix. add output method helper class

Add method for extraction of attempts, add comments
Bug fix
Use of constant fields, add output method
Change when solution is zipped

Solution is zipped immediately after it has been handed over
so it can be downloaded anytime.
Add capability for source codes download

With sufficient privileges user can download their own or others source
codes.
Update gitignore

Add data folder to ignore list.