Feat/detect voice activity

[felipem1210]

Closes #18

• Implemented new channels playingAudioCh, userBeginSpeakingCh and audioInterruptCh to determine when person began to speak while playing audio, and setting an interrupt flag so the audio stops playing
• Implemented new go routine to set this interrupt channel
• Changed the sendAudio function to read from the interrupt channel and cut the audio play. Also the sendAudio is executed as a new go routine so it does paralel the play and the audio process from asterisk.