Implement componentWillUpdate method for TranscriptEditor component

[alexnorton]

To address performance issues the React componentWillUpdate method should be implemented for the TranscriptEditor component such that re-rendering only happens when the transcript has changed.

[haslaa01]

I believe that the shouldComponentUpdate should be used in order to prevent the component from re-rendering.

https://facebook.github.io/react/docs/component-specs.html#updating-shouldcomponentupdate

[alexnorton]

@haslaa01 right you are 👍