popover should include horizontal direction

[Progdom]

currently the popover will open right of the target that opens it. This should be configurable to open left, right, up, down, etc. It should also be smart enough to know when it's reached the edge of the window. It currently opens to the right, OFF the screen and has no ability to open to the left of it. This makes the component unusable for targets that sit on the right side of the screen.

[Progdom]

I've created a gitter room for this project. https://gitter.im/p-angular2-mdl-ext/Lobby?utm_source=share-link&utm_medium=link&utm_campaign=share-link You can talk to me on there. You should create an official one for your project. Mine is based off my fork. It's free :)

[AVykhrystyuk]

Hi, I have made a PR to make popover position to be configurable same way as it is for mdl-menu component.
Could you please take a look?
#1082