java.lang.AssertionError: Contrib qn giver type invalid: TEAMS expected: but was: #2383

Fixes #2383
Removed asserts for invalid giver/recipient, force values to be valid, log as severe and show error to user instead.
Disabled invalid options, since hiding does not work on some browsers.
According to w3schools: In XHTML, attribute minimization is forbidden, and the disabled attribute must be defined as <input disabled="disabled" />.

Those with disabled="" are done by jQuery, using .prop('disabled', true), which does not follow that convention.

Should all occurrences of this be changed to simply the disabled tag?