Make plugin responsive

[imakewebthings]

Responsive in the design sense. The width of the plugin and books should be determined by the width of its container and not fixed-width.

[imakewebthings]

I have the bulk of this done in a local branch. The way I'm tackling it is by removing the height_multiple and replacing it with a min_height_percentage and max_height_percentage. We already have a min height and max height (20-39 by default) so the book height value is just translated from this range to the percentage range. Right now the min and max percentages are 59 and 100 respectively. So a book height of 20 results in 59% width, a book height of 39 is 100% width.

In a lot of our demo data the book heights are close together, not straying far from the low end of the height range. The resulting percentage translation makes the book heights more similar than before. It seems that a book on the high end of the range would have broken out of the demo width anyway, so this is to be expected.

We could tweak either of the ranges to change the way this looks, or switch to defining the raw height range using the actual data set min/max instead of predefined ones (so 100% == the tallest book no matter what, min% == the shortest book no matter what) though that comes with its own design considerations (books look different depending on the data it's pooled with).

Merging this is probably still a ways off, since there are other issues ahead of this one. We can revisit this when it becomes relevant. Food for thought in the meantime.