Make max-height computation more stable

Instead of setting the parent's height as max height of the
<img> element, find the first parent which has a non-automatic
height (that would be .mw-mmv-image-wrapper).

With the old structure, the height of the parent element could
be determined by the height of the image, which would then be
written back into the max-height of the image, messing up the
aspect ratio. I did not see this in the wild, but it was easy
to reproduce by changing the timing of the resize handler (in
particular, I tried to call the resize handler before loading
the new resolution, to make the UI more responsive, and ran
into this problem). This cannot happen anymore now.

This also fix a bug on some browsers (IE 10, maybe iOS Safari)
where the size of the image could be slightly larger than the
available space, and the bottom of the image was obscured by
the metadata panel. I am still not sure how exactly that
happened, but it was related to the <img> parents with automatic
heights having incorrect height. After making sure the <img>
has a max-height derived from an element with non-automatic
height, I cannot reproduce the bug on IE 10 anymore.

Change-Id: I193aefc42e6d6072717643659a9e4c0c8b7c7e93
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/698
Bug: 66244
Merge "Make max-height computation more stable"