Add state to splash screen (Issue 57)

[jama5262]

What is the Purpose?

Add state to splash screen

What was the approach?

Added get and set functionality to the Preferences interface and add implementation to edit the splash screen state in the PreferencesImpl class

Are there any concerns to addressed further before or after merging this PR?

Also decreased splash screen animation duration by half

Mentions?

@wangerekaharun @michaelbukachi

Issue(s) affected?

#57

[wangerekaharun]

Looks Great,

One request however, though this should be on the previous PR, can we have the documentation on how to add functions to the Shared Preference Implementation class in core on ReadME

[wangerekaharun]

Setup state in SplashScreenActivity

[wangerekaharun]

@jama5262 am merging this, you can work on the documentation part and reference it to #4