Fixes of webkit audio filters for Chrome 36.0.1985.125

I have fixed the bug with Chrome 36.0.1985.125 (https://github.com/ejci/Chrome-Audio-EQ/issues/9).

webkitAudioContext.createGainNode() was deprecated and renamed to webkitAudioContext.createGain
Details here: https://code.google.com/p/chromium/issues/detail?id=395130

There was also some changes in webkitAudio, filter types for example, so I made some changes on filters too.
Also code was refactored a little.