Updated CSS & JS Injection, Changed UI behavior

I'm not filing this pull request presumptuously--I merely wanted to share in case you were interested in merging my changes. They are as follows:

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## CSS & JS Injection Changes

CSS and JS are now injected once regardless of how many Font Awesome fields are on the screen. Also, CSS and JS are using EE-accepted methods for injection.

## UI Changes

![screen shot 2014-07-25 at 1 47 31 pm](https://cloud.githubusercontent.com/assets/868631/3706721/41c8a50c-142c-11e4-9eb1-2e56919949d8.png)

The UI now shows a list of all options when the input is in focus but empty. This allows for simpler icon discovery. Additionally, the selected icon now overlays the input (making it look inline with the icon name).

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Again, no offense taken if you reject this pull request. Thanks for your work on this add-on!!

Mark