Adding support for theming the Rocket.Chat app for iOS

The Rocket.Chat team for iOS has been working on improving the UI, and is planning to come out with a major app re-design for version 2.3.0. One of their goals to support this redesign is to add the ability to theme the application.

My project for the summer will focus on theming the application whilst introducing a minimal amount of impact on the rest of the code base.