Change the style of touch feedback

[gnprice]

Currently when you touch a button, or an item in a list like the inbox screen or streams screen, we use Material Design's "ink splash" effect to give feedback showing you what you touched.

@terpimost writes at #339 (comment) :

I don't assume we have material UI components and their tap animations... I suggest to not bring it to iOS version at least.
I think it is ok to darken the hit area or a button on tap. We can also scale down the button a bit as a default option. It is also ok to not bother for the smaller elements which user might not even see under the finger.

So we can try one of those instead.

Whatever effect we choose (or suite of different effects for different situations), we should test to see we're happy with how it behaves not only on buttons, but on those list items like a stream on the streams screen or a conversation in the inbox.