Keep up-to-date SelectRestriction information in each event marker node.
Inject values and trigger event handlers in the correct sequence.
Support dynamic select box constraints.

We keep track of any updates to the available options of each select box as we interact with the form, and use a set of possible values which is appropriate for where the injection appears in the execution tree.
Merge branch 'feature-select-element'
Fix a bug in the concolic test suite since the string->int optimisations.
Fix some incorrect assertions in a test case.
Merge branch 'master' of github.com:cs-au-dk/Artemis