fixed mixeval zero mark bug

When the zero mark option is selected in the mixeval template,
the weight of each descriptor is shown correctly in the add and
edit view. However when we view the template in the view and
student mixeval_form, the zero_mark selection is ignored.

I've patched it up by modifying the conditions for the zero_mark
option to be used.
Update version to 3.0.4
Fix failed to add user when user data has tab (\t) in API
Fix a style issue
Fix SurveyInput model test missing user_tutor table
Fix failed tests and missing fixtures
Moved API log into logs/api.log
Fix #480, removed auth error on login page when redirect from app root
Fix non-existing users added to group as id 0 by API

When using API to add users to group, non-existing users will be added
as ID 0 to the group. Now iPeer ignore those non-existing users.
fix zero_mark bug for rubric view and rubric evaluation forms
Fix a bug when adding 0 member to course using API
Update guard plugin
modified groupMembers and enrolment in the api

For groupMembers, I have changed the reaction to adding a group
member that is not in the course to skipping the user from terminating
the request. I have also added the task of removing members that
are not in the new list.

for enrolment, I have changed the reaction to enroling users that
do not exist to skipping the user from terminating the request.
Similar to groupMembers, users already enroled in the course but do
not appear in the new list would be removed.

I have added tests for the api to test the changes mentioned above.

Conflicts:

	app/controllers/v1_controller.php
	app/tests/cases/controllers/v1_controller.test.php
fixed a bug in the api

The api has a small bug for enrolment where the classlist may not
be complete if any of the ids in user_tutors, user_courses, and
user_enrols tables are the same. This has now been fixed by
using array_merge instead of the union operator (+).
fixed the broken api tests from the previous commit
Merge branch 'hotfix'
Bump version to 3.0.6