API improvements/breaking changes: NewXyzCommand should not need commandID

[longquanzheng]

This includes:

• NewTimerCommand
• NewSignalCommand
• NewInterstateChannelCommand

Most of the time people don't need to use commandId.

We can create new APIs for using commandID:

• NewTimerCommandWithId
• NewSignalCommandWithId
• NewInterstateChannelCommandWithId

[longquanzheng]

Alternatively make NewTimerCommandByDuration NewSignalCommandByChannel etc