feat(datepicker): add optional force-position attr

[hxtpoe]

Specify where the datepicker element should be displayed

[hxtpoe]

@rvanbaalen could you look at the PR in free-time? That is the next time when I need this feature, so I've decided to implement. Let me know if you've got some suggestions.

[wesleycho]

I think just calling it position would be fine.

[wesleycho]

History needs to be fixed, there is pollution from what appears to be other repositories. The base branch should branch directly from master on this repository, not any other.

[hxtpoe]

-history fixed
-CS fixed
-attr name changed from force-position to position and options renamed

@wesleycho could you take a look?

[wesleycho]

I'll take a harder look later today - my only main point of concern here is multiple PRs dealing with positioning but not implementing the feature in $position itself. I may look at tackling the positioning issue in $position so we do not run into these edge issues in each component & duplicate the logic.

[wesleycho]

Thinking about this, I believe that the API should be tweaked to support single directions as well, i.e. top, right, bottom, and left. The attribute should take a string, i.e. top left to specify top and left, or top for just top (among other possibilities).

$position.offset should take an optional second parameter that takes a string of the form described above and parses it to determine how to set the offset. It should behave as it currently does otherwise. This portion should be in its own PR.

[wesleycho]

Doing a little more investigation, $position.offset should not be modified - I am in the process of investigating an appropriate modification in $position to accommodate the proper approach in the datepicker for this feature.

I should have a PR ready by tomorrow with that modification.

[chrisirhc]

Looking forward to $position changes. I agree that the feature should be on the $position service itself. Thanks @wesleycho .

[icfantv]

Closing in favor of #4762.