report: split methods into accessors and mutators in overview

[d-xo]

When auditing a contract it is useful to have a full overview of all methods that can be used to mutate state. The method list overview in the report currently mixes accessors and mutators, making it a little harder than it needs to be to get this information.

It would be nice if there would be some split or visual differentiation between methods that mutate and those that don't. This information could be extracted from the specs, as methods that mutate have their <static> cell set to false.