Dan Poltawski authored Apr 01, 2015 and Eloy Lafuente committed Apr 02, 2015

This reverts commit 19ffcbe2, reversing
changes made to 2112dd44.

Conflicts:
	lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor-min.js

Conflicts:
	lib/db/services.php

Conflicts:
	lib/db/services.php

This removes the need to write tempfiles in these locations.

We now abstract the actual file generation to a new function.
We are then able to call this function from the other image generation
sources. This allows us to generate thumbnails in a more efficient manner.

* Stored files stay as stored files and are not temporarily re-written to
  disk;
* Strings containing an image remain as a variable and are not temporarily
  written to disk; and
* Arbitrary files are not captured to string.

Conflicts:
	lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor-min.js

This feature is designed for use on pracice or formative quizzes.
It is available for quizzes that use Interactive or Immediate feedback
behaviour.

If the teacher turns this on in the quiz settings, then once a student
has finished a question, they get a 'Redo question' button beside the
question. If they click it, then the question they finished is replaced
by a new one so they can try again to practise that particul skill or
bit of knowledge a bit more.

When randomisation is involved, the studnets will be given a question or
variant that they have not seen before if possible.

Conflicts:
	mod/lesson/db/upgrade.php
	mod/lesson/version.php