Compare the content of the slide divs

[ElliottLandsborough]

Separate pull request because this might be an extremely inefficient way of achieving what is required. I'm not very confident with anything DOM related so there might be a better way to detect changes in the slide contents.

This patch:

1. gets the innerHTML of any slides that have already been initialized
2. Puts them into an array of strings
3. Compares them to the ones that may have been added which have triggered 'componentDidUpdate'.

If the old/new slides are different the statement validates as false so the return statement is skipped.

[ElliottLandsborough]

https://github.com/alvarotrigo/react-fullpage/issues/157

[alvarotrigo]

Why closed?