Fix missing sms system prompt

[andr5w]

Fixes an issue where the system dialog for selecting a default SMS application did not appear on some android systems when a user taps "Import Messages".

[andr5w]

This should fix #167.

[tmo1]

Thank you! I should have added the <uses-feature> element a while ago, since Android Studio was urging it.

Regarding the exported value for .ComposeSmsActivity, for some reason the official documentation doesn't include the exported attribute at all, so I suppose that when I added it, I went with false, but I see that Fossify has true.

Did you test these two changes separately to see which one fixes the problem?

[andr5w]

No worries. Setting the exported value for .ComposeSmsActivity to true fixes the linked issue. I added <uses-feature> for the same reason you mentioned - it's not required for this fix (I did test this) but I figured it'd be a good inclusion from a maintenance perspective.