Don't propagate touch to items behind a header (update StickyRecyclerHeadersTouchListener)

[alexcohn]

When a sticky header is touched, a regular item behind it may receive the ACTION_DOWN event, and display "pressed" state. This commit fixes such undesired behavior by returning true for onInterceptTouchEvent() if it was DOWN inside the borders of a sticky header.

[jacobtabak]

Thanks! I'll test it out and update the sample to demonstrate the fix and then merge sometime soonish.

[alexcohn]

See the "demo" at alexcohn@73d9e9a

[jacobtabak]

Thank you so much for pushing the updated sample. It really helps! I verified your fix and it works as expected.

We'll need to fix the indentation to match the rest of the project. Also, I think it would be great to add some javadocs here to explain what's going on. Would you mind doing that? I'm happy to do it if you're busy.

I'm planning on investing some time down the road cleaning this whole project up, adding checkstyle & tests to CI, and enhancing the documentation. So any documentation that we have now will make that process easier.

[alexcohn]

I would prefer if you take care of javadoc, to keep it all styled consistently. Regarding indentation, spaces, etc. feel free to fix

[jacobtabak]

Thank you again! I'll touch up those things and we'll merge & release.