Time to bump minSdk to 16

It was about time: API levels 14-15 are falling behind pretty quickly.

We can see in this image, from a sample of about 200k sessions, how the 4.0.+ accounts for only ~6% and rapidly decreasing.

It's not that I particularly need any API introduced in 16 in a daily basis (except maybe using fontFamily as it is intended to be done), but if we don't keep pushing we will be forever stuck in 14 as we were for years in 8-9.

So, let's go for it and use API 16 as minSdk for the next projects! :)