ReportbackItemDetailView -(CGFloat)heightForWidth:width

[aaronschachter]

Closes #697 - renders Reportback Items with dynamic height in the Campaign Detail view controller.

Instead of using iOS self sizing cells, we manually calculate the height based on xib values in a new -(CGFloat)heightForWidth:width method.

I've been fighting with getting a sizing cell to return the appropriate height (#687, #688, #694), but it keeps returning sizes that are too large (and the results vary upon each load, making it even trickier).

Reviewed with @pixelrevision -- using good ol' math (similar to what we're already doing in the LDTCampaignDetailViewController sizeForCellAtIndexPath: iimplementation) seems just way more understandable and maintable at this point, vs fumbling around in the dark trying to get autolayout to magically calculate the numbers via layoutSubviews, layoutIfNeeded, etc.

[aaronschachter]

Would make sense to remove the displayShareButton functionality and related hide/collapse to keep things tidy, as we're just manually determining whether or not to show it based on the height we return in -(CGFloat)heightForWidth:width

[aaronschachter]

Going to keep the hide/collapse functionality in for now, as it could come in handy for kudos/props (#621)