add optional callback parameter for unit testing `setButtons`
add optional callback parameter for unit testing `setButtons`

Electrode-iOS/ELHybridWeb,TheHolyGrail/Zoot,kuruvilla6970/Zoot,kuruvilla6970/Zoot,kuruvilla6970/Zoot,Electrode-iOS/ELHybridWeb,TheHolyGrail/Zoot