Improve full-window layout height calculations

[msmolens]

Both Lesion Images and Annotation Study Results use full-window layouts. A key part of these layouts is setting the height of the main content container so that it fills the available space without necessitating a vertical scroll bar.

Currently, these heights are calculated by subtracting a fixed value from the viewport height. These calculations are sensitive to changes in height of the header or footer. Additionally, the existing calculations are even consistent, perhaps due to margin/padding differences in the content.

A better way to determine these heights should be investigated.

References:

https://github.com/ImageMarkup/isic-archive/blob/0f80ace9da83b7c8797f6d8f4b37bce52a7a545e/web_external/stylesheets/body/studyResultsPage.styl#L6

https://github.com/ImageMarkup/isic-archive/blob/99212af4ac7caf86d03ae9cb754df42a27ab2b05/web_external/stylesheets/body/imagesPage.styl#L16