Further parsing improvements

[xtrojak]

• [ ] allow multiple regulations to be defined in a single model
• [ ] #86
• [ ] #15
• [ ] user should be warned if a rule is not well-formed, i.e. agents on corresponding positions in LHS and RHS have different names
• [ ] warn on senseless rules, i.e rules doing no changes
• [ ] highlight all numbers inside rate expression (number five is highlighted here 5 + var but not here 5+var)