Use ACTION_SENDTO in EmailIntentSender

The use of `ACTION_SEND` in `EmailIntentSender` causes the `Intent` to resolve to not just email apps, but also *Skype*, *Google Drive* or *Bluetooth*, to name just a few. While this might be desirable in certain cases, the name `EmailIntentSender` clearly implies that the report is to be sent via email only.

Using `ACTION_SENDTO` in conjunction with a `mailto:` URI as the `Intent`'s data makes it resolve to email apps only (*Email* and *Gmail* in my case).

Tested on: Android 4.4.2 Stock (Nexus 4) and Android 2.3 Stock (Emulator)