Update Simple Mail App

Added click-and-send functionality to demo mail-app to demonstrate use of Actions with SDK.
Added a couple OptionsMenu items to help manage login and clearing token cache for testing.
Removed a couple helper classes to make code as simple as possible.
Changed logo to modern Exchange logo.

![screenshot](https://f.cloud.github.com/assets/4421720/2398921/429a8c9e-a9fa-11e3-9f12-574051ae2652.png)