handle :native_or_unimrcp renderer in #execute_command

Adding a new switch for :native_or_unimrcp allows us to play audiofiles
natively and TTS via unimrcp for ASR question types. Previously, only
DTMF question types handled :native_or_unimrcp appropriately

Files affected:

- lib/punchblock/translator/asterisk/call.rb
- spec/punchblock/translator/asterisk/call_spec.rb
allow :native_or_unimrcp as a valid renderer

previously, only :unimrcp passed the validation step

Files affected:

- lib/punchblock/translator/asterisk/component/mrcp_prompt.rb
- spec/punchblock/translator/asterisk/component/mrcp_prompt_spec.rb
[CS] reduce duplicate code by testing invalid renderers in same context

Files affected:

- spec/punchblock/translator/asterisk/component/mrcp_prompt_spec.rb
Merge branch 'feature/ast_tts_fallback-asr_support' into develop

Prepare to submit pull request, merging the Ifbyphone patch into the core develop branch.
Update spec

Update spec for changes specific to bleeding edge Punchblock. The
proposed code changes remain the same.

modified:   spec/punchblock/translator/asterisk/call_spec.rb