Transform any color strings with processColor, use color numbers internally

[abrahambotros]

• To be compatible with a variety of color strings (as most other React Native components do in their style's color parameter), we need to call the built-in processColor function provided by React Native. We can then pass the resulting color number to Android Color directly, and can use RCTConvert on iOS to convert it to a valid #AARRGGBB string for UIColor.
• Also add .gitignore from recent React Native project version.

In addition, this should fix https://github.com/maxs15/react-native-spinkit/issues/42, even though that issue is technically already closed. @AlisonWonderlandApps