[#61] Rename integrational interpreter

Description

Words "interpreter", "interpret" and such are a bit ambiguous in our code. There is Michelson.Interpret which interprets one contract (one may say it interprets a sequence of instructions against given stack) and there is Michelson.Runtime which also uses "interpret(er)" words. It leads to ambiguity and confusion. For instance, there are types with very similar names such as InterpretError and InterpreterError. This MR proposes renaming all appearances of "interpret" with "executor". I'm sorry for these all merge conflicts that'll be caused in a future.

Related issue(s)

Resolves #61 (closed)

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