Identifier tracking

[LinqLover]

Track objects through the program trace by their identifiers. Be stricter than object identity here.

Examples:

• Extract/highlight all contexts in a trace that
  • "move" a variable under a given name (dataflow, push/pop it from/to the variable stack, assign it to variables, pass it to other objects via a message, return value of message send/primitive)
  • "see" a variable under a given name (i.e., have access to it, even if they do not actually move it)
• self submorphsDo: #flash -> Symbol>>value:, Symbol>>#value:, ...
• Support for Better filter mechanisms ("through filters") #73
• Explain side effects in a sandbox (cf. Add prototypical Protocol Explorer LinqLover/SimulationStudio#39)

Current state:

• A first very incomplete prototype for scopeless tracking exists.
• Next steps: Discuss use cases and requirements in detail, extend prototype
• Decide on whether this should be implemented in the scope of SimulationStudio or TDB