Set horizontal alignment of popovers

[jrubenoff]

Outcome

This should be possible:

Custom classes for each button (primary small and small), aligned to the right edge of the link.

Structure

Popovers should have options for...

• Whether the popover is aligned to the horizontal left, right, or center of the object. (This will also dictate the caret's horizontal position. For top and bottom-aligned popovers only.)
• The class(es) of the primary button. (Default: primary)
• The class(es) of the secondary button (Default: "no class")

Also, we should remove delete_ from some classes (like popover_delete_confirmation_message to get rid of code smells.)

[ajb]

This is done, with the exception of the alignment, which would need to be addressed in Bootstrap. I've marked it as "hold".

I can suggest positioning workarounds on a case-by-case basis.