MDL-40457 Question Bank: Allow plugins to add columns

Allows plugins to add columns to the question bank view by extending question_bank_column_base.
The plugin should return an array of its columns from *_question_bank_column_types().
Columns to display are set in $CFG->questionbankcolumns.
MDL-40457 Whitespace fix
MDL-44106 add WS_SERVER constant to all web service calls

This will help us hack around some nasty webservice problems,
such as require_login() and it will be used to set proper 'ws' origin
in logged events.
MDL-44106 add origin info to $PAGE object and use it in logs