Feature: baked-in dragging features

[willshowell]

Some api notes

1. enable/disable
2. snap back to anchor with/without animation
3. Probably relies on Feature: backdrop options #9 since dragging is sort of predicated on the idea of interacting with content behind it (completed)

[willshowell]

This may also work better as a globally positioned popover with draggability as an input

<sat-popover global draggable top="40px" right="40px">
  <!-- ... -->
</sat-popover>

It would mean that anchors are optional when global is specified. Another option would be to make a new component that opens itself wherever in the viewport.

<sat-global-popover #gp [draggable]="movingEnabled" top="40px" right="40px">
  <!-- ... -->
</sat-global-popover>

<button (click)="gp.dock()">Return to original position</button>