UPG-39: Checking in platform-based icons and screenshots.

Checking in platform-based icons and screenshots to the images directory.

Images added to the following directories:
/src/images/platform/android
/src/images/platform/ios

The screenshots added might be helpful to individuals setting up Google Play or Apple Stores. Both stores require screenshots and the attached screenshots could act as placeholders. If these are not valuable or used by anyone we can certainly remove them from the code base.