[Ch21 - update] Wired Send Button

Added:
+ wired up Send button to fire implicit intent

Notes:
+ <intent-filter> is used in apps that would be used given a specific
implicit intent; i.e.:<action android:name="android.intent.action.VIEW"
/>
+ in addition, this line must be explicitly stated: <category
android:name="android.intent.category.DEFAULT" />