Chart self-checks

There are a couple of simple checks that the designer can easily perform locally to avoid sending the chart outside of the designer for analysis. These checks include:

• cyclic parent-child relationships
• illegal transitions between AND states
• dangling transitions (missing/unknown target or source)
• no outgoing transitions from a pseudo state
• an ingoing transition to an initial state
• no outgoing transition from an initial state
• transition label from prob pseudo state doesn't match /@0?.[0-9]+/
• transition label from choice pseudo state doesn't start and end with [ and ] respectively
• child visually not within the bounds of the parent
• state visually inside another but is not a child of that state
• missing initial state

All of which should trigger messages described in #5.