Handling overflow on realignment

[jcdang]

I noticed that the current implementation doesn't handle new placements well when receiving a realignment. I started off with trendmicro's implementation but ended up rewriting a lot of it based on my needs. Here's the code for what I've done. Feel free to integrate any of it back in.

Gist

• removed dependency on rc-align and used dom-align directly
• handled placement realignment based on angle positioning of the popover and target

Thanks for the great work!