Remoce trace aggregation from TraceDisplay in preparation for the native trace summarisation in the execution tree itself.
Add new TraceConcreteSummarisation node type.

This node type si created instead of strings of TraceConcreteBranch and TraceFunctionCall nodes.

It does not yet support merging two traces where a concrete branch is explored in both directions. The trace merger is not yet updated to deal with the new node, so it will not detect any divergence within a concrete summary.
Allow concrete summaries to handle multiple concrete execution paths.

This allows us to model a fully-explored concrete branch within a concrete summary. We make the concrete summaries into a new node type which can be an N-ary branch in the tree if this happens.

Not tested thoroughly yet but seems to be passing the simple concolic tests ok.
Updated to latest CVC4 with some string and coercion improvements.
Disable divergence dumps again.
Fixed a bug in the trace statistics calculator.
Merge branch 'feature-select-element' of github.com:cs-au-dk/Artemis into feature-select-element
Add a test case for dynamic form options modification and fix an issue where we generate invalid constraints for an empty select box.