create a download page for TBA on torproject.org

At:

We should add:

'[android logo] Android'

Option at the menu [see screenshot download-01 attached]

Change the download easy page for Android to be Tor Browser for Android instead of Orbot:

The link that goes to this page comes from the little menu on the right [see screenshot download-02 attached]

Download button should link to apk build and we should include a link to the package signature as well, just like we do for the other ones.

There is no need for a language selection option, as this build is not yet localized.