Integrate structure-based editing

[soerendomroes]

See
#134
kieler/KLighD#156
kieler/semantics#84
kieler/pragmatics#9

Identified TODOs:

• Context menu entry validation: If one enters a wrong expression as a guard of name it should be visible. Entering the incorrect statement should not just result in an error.
• Typo in Semantic
• For the Add Region Action: Rename "State Name" to "Initial State Name" and change the order of state and region name entry
• Optional parameters should be definable as optional in the synthesis.
• The context menu should show that an entry is optional/mandatory, e.g. by adding "(optional)" to the text field header
• Autofill region name with name of parent state
• Use enumerations instead of Strings in StructuredEditingMsg.
• When selecting a second element (e.g. the edge target), the selected element should be highlighted and this should be filterable semantic elements and hierarchy. E.g. only edges in the parent can be selected.
• No error messages check everything beforehand
• Not all context menu actions are correct: Check whether the action actually produces the correct behavior in that context
• Does not work in klighd-cli. The same problem exists for interactivity. The server needs to adjust the model directly in this context instead of asking the client to do it.