Email Attachment support for Android

Hi Stuart,

I have implemented the code to send an attachment in Android.

Because I need access to the Activity (to store files in a way the email program can access the file, that was the hardest thing to do), I have made DoOnActivity protected (was: private) in MvxAndroidTask. An alternative is to do the resolve to IMvxAndroidCurrentTopActivity myself.

With this code you can send only one attachment (that fits best in the most standard Android email implementation for email apps).

Best regards,

Hugo