Add comprehensive unit tests for LFVM's interpreter

[HerbertJordan]

This issue is closely related to #751
Refined responsibilities for the interpreter tests are:

• different configurations (normal mode, step-wise, statistics, logging), evaluate the following:

  • TestRunWithLogging
  • TestRunBasic -> TestInterpreter_Vanilla_RunsWithoutOutput

• Stop conditions: end of code, stopping codes, error triggered

  • TestRunReturnsEmptyResultOnEmptyCode rewrite to test reaching end of code (and case for empty code)

• stack bounds violations

  • TestInterpreter_step_DetectsLowerStackLimitViolation
  • TestInterpreter_step_DetectsUpperStackLimitViolation

• static gas costs

  • TestContext_useGas_HandlesTerminationIfOutOfGas use gas handles no termination any more
  • TestStepsFailsOnTooLittleGas rewrite to tests static gas costs.
  • TestInstructionsGasConsumption move to instructions tests

• Detects non-executable code

  • TestStepsDetectsNonExecutableCode

• error/state propagation

Add/check unit tests for context utilities:

• useGas
• stack limits check
• getOutput
• generateResult

Responsibilities which are to be handled in #751 (therefore not in interpreter tests):

• minimum required revision
• static-mode violations
• jumps are correctly processed (JUMPDEST)
• context calls are issued

Tests to be migrated to instruction tests:

• TestStepsProperlyHandlesJUMP_TO
• TestStepsDoesNotExecuteCodeIfStatic