md-menu: saves position on first opening and does not position according to target item on windows resize

[kschwidder]

Problem:
It seems that md-menu is saving the internal absolute position from the first opening instead of the current item. Therefore on resizing the window the menu is misaligned with the target.

Scenario:

1. Open md-menu and close it again.
2. Resize window to min or max.
3. Open md-menu again. It will show up according to the first absolute position and not according to the given target

[jozsi]

+1

[MrBlenny]

Additionally, if you scroll the menu stays fixed on the screen and does not scroll:
http://i.imgur.com/1JxnbVu.png - view when not scrolled
http://i.imgur.com/OcT5A6l.png - after scrolling

The position of the 'md-open-menu-container' should be changed to absolute?