Make callouts in the app more like Apple Maps' callouts

[justinanderson]

• Support arrows on the left/right.
• Support animating from one size and arrow position to another. Apple Maps on iPad does this.

[loganwright]

@justinanderson - I tackled a lot of the popover stuff in the latest PR, I'm waiting for Ross to dig in to the specifics so that there's a second set of eyes making sure everything is readable and well organized.

Once you take a look, all of the drawing parameters should be easy to adjust, ie: arrow size, positioning, rounding, etc. I think this implementation cleans up a lot of the problems associated w/ SMCallout and is much more reliable with custom content views. Any features you're missing shouldn't be hard to add at this point.

I do have some questions about the animation. I was looking at Apple's implementation, and it seems to have a very specific set of events. The popover is always arrow down w/ text, subtitle, disclosure, and occasionally a left side image. This then animates to a very specific view controller that is always positioned left or right. I'm having a hard time thinking of a way to generalize this behavior to create a 'drop in' solution for this. Do you have any specific examples in the app that you'd like to see animated? I think this would be easier for me to implement a specific circumstance than something more general.

[justinanderson]

@rosslebeau

• The callout's arrow should be the rounded style instead of a hard triangle. We have images that can be used for it already, though they're only in the repo's history: [1] [2] And the MITPopoverBackgroundView class already contains logic on how to draw arrows at any point and edge of a popover using those images. Shouldn't be hard to reuse it for callouts.
• The disclosure indicator needs to be the right artwork too. Dark, thin, small, with the right amount of padding. Light, thick, not enough padding.
• Something about its sizing math is off. It's allowing overly wide callouts
  instead of wrapping contents.
• Should also be limiting which arrow styles are possible. Left and right side arrows shouldn't be possible on iPhone layouts.