Check the version of the Maxima library code used.

Since we have mechanisms like MaximaPool and maxima-optimised, it is
possible for the version of the STACK Maxima libraries being used to get
out of synch with the version that is shipped with the STACK question
type.

Here, we make every STACK evaluation report the version of the libraries
used. (It really needs to be every evaluation, since this is then stored
in the cache, and we would like to know when the cache gets out of
date.) We then check the version matches what is expected, and if not,
report it in two ways: 1. into the server's PHP logs, and 2. on the
healthcheck page.
Refactoring of the potential response tree for more nuanced use of simplification.  Inputs to question tests are no longer simplified.
First pass at reporting scripts
Answer notes added to reporting.
Code tidy
Minor update to the docs.
Added a table to show answer notes by question note, i.e. do particular versions result in disproportionate outcomes?
Fix things broken by the stackmaxima version checking.
Merge branch 'master' of github.com:maths/moodle-qtype_stack
Allow RANDOM_PERMUTATION
Define stackmaximaversion during installation.
Merge pull request #50 from kabalin/master

Fix stackmaximaversion issue
Fix feedback display when non-quiet answer tests are used.
Added question note to fields in which delimiters are automatically fixed.
Make instant validation work for matrices.
Fix matrix instant validation in IE and Chrome.
Fix broken unit test.
The replacedollars script missed out hints.
Validate hints.
Minor fix to the feedback given by the factored form answer test. [Note first Maxima version change]