Allow customization of fonts, text size, etc

[daviesgeek]

It would be really nice to allow customization of all the options that are in InAppSettingsConstants.h so that the UI can be customized to fit a certain app's UI scheme.

Note: I am a rather new Objective-C/Swift developer, so I don't know exactly the extent of refactoring that this will take to implement. I am going to dig into the source code to figure out what's happening, and see if I can submit a pull request with the changes. Wish me luck :smile: