Initial rendered map does not cover full viewport

[jumpinjackie]

This has actually been a long-standing problem which I've known, but it's criticality has been bumped up as a result of the new selection highlighting feature.

To reproduce this problem, view the demo Sheboygan map (but one with watermarks). The watermark configuration states to show the watermark on the bottom right, but the initial view of the map miscalculates the viewport dimensions resulting in a reduced initial map image.

Attached is a screenshot demonstrating the problem.

This may also be tangentially related to #118

If this initial view has selectable layers/features, the sub-selection will be displaced as it will be loaded into a OL static image source that actually covers the full map viewport.