Fix labels around border

[Rdornier]

Resolves #614, resolves #615

[will-moore]

better to use border = panel.get('border') which won't cause an error if border is missing

[will-moore]

The app JS fix looks good.

The PDF labels are shifted OK for single labels in some positions, but where we have multiple labels (e.g top right panel) or labels on the inside corners then it's not looking right.
Also left-vertical labels (bottom-left panel) is too far left.

Screenshot shows app (top-left), PDF with this PR (top-right) and PDF without this PR (bottom). All borders are 15 px:

[Rdornier]

Hello Will,

Thanks for you careful review. I've made a fix to correct that.

There is only one remaining thing. When you re-open the figure, with vertical labels on panel with borders, the vertical labels are very far away from the panel. If you move the panel, then the position of the labels are correctly updated.

I found out that this behavior is coming from those two lines

            // need to force update of vertical labels layout
            $('.left_vlabels', self.$el).css('width', 3 * self.$el.height() + 'px');
            $('.right_vlabels', self.$el).css('width', 3 * self.$el.height() + 'px');

If I remove them, this behavior disappear. But I don't know if I'm allowed to remove them, as they should be needed for something, right ?

Rémy.