include format_singleactivity in core

Test 1 - upgrade with existing plugin.

1. On Moodle 2.5 or 2.4 (either one is enough) install format_singleactivity from plugins database
2. Create a course in "Single activity" format
3. Backup this course, save the backup file
4. Upgrade to master (remove folder /course/format/singleactivity first)
5. Make sure there are no errors, course is still operational
6. Restore the course from backup made on previous version, it should restore the content (maybe with version warnings).

Test 2 - creating the course

1. Create a course in "Single activity" format, select any activity type in course settings
2. Proceed to the course, make sure you are redirected to add activity page, do not create activity
3. As a student try to access the course, you should see the empty course
4. As a teacher try to access the course, make sure you are redirected to the create activity page
5. Create an activity
6. Make sure student can access it
7. Make sure the navigation menu looks right, everything inside the activity is accessible

1. Create a course in "Single activity" format, select "Label" as activity type, add module (alternatively add folder that is displayed inline)
2. Make sure it is accessible by both student and teacher correctly

1. Create a course in "Single activity" format, select "Database" as activity type (or any other type that extends the module navigation), add the module itself
2. Make sure it is accessible by both student and teacher correctly, navigation menu is extended for the module

1. Enable Assignment 2.2
2. Create a course in "Single activity" format, select "Assignment 2.2" as activity type. It requires subtype (now not recommended but not completely deprecated)
3. Teacher is not redirected to the "Add activity page", the empty course should be displayed instead. Teacher can turn the editing mode on and add module.
4. Make sure it is accessible by both student and teacher correctly

Test 3 - changing the course format

1. Create a course in any other format, add several activities to it
2. Edit the course setting and change format to "Single activity", specify the activity type (ignore the warning about extra activities)
3. If the course had the activity with this type it should become the main, otherwise teacher should be redirected to "Add activity" screen.
4. Make sure all redirections look all right, all other activities are accessed in course navigation as "orphaned", and they are not visible to students.

Test 4 - hidden activity
(this bug was recently reported for this format, let's make sure it is fixed)

1. Create a situation when the main activity in the course is not visible to the student (either remains hidden after changing the course format or edit the activity settings and make it hidden or add conditional access, etc).
2. Try to access the course as a student, make sure everything looks ok

Test 5 - backup and restore

1. Backup course in "Single activity" format
2. Restore it as a new course, into the same course, make sure everything works fine