Update view state using Reactive Cocoa

[callzhang]

• In SleepView, the state of sleep-able and non-sleep-able should be controlled by RC, current implementation is clumsy
• In SleepingView, the wakeup/cancel button should be bind with RC too
• The wave movement should be attached to player's volume, not recorders'

[caoer]

finished first 2. @callzhang what's the last one: "The waveform should show and play when AVManager.player.isPlaying == YES"

[callzhang]

Forget what I said, I found the reason that it looks odd: The wave movement should be attached to player's volume, not recorders'. Current implementation only attached to the recorder, so the strength is constant, which is undesirable.

[caoer]

@callzhang ok, closing issue.