Fix for #245 - Images no stay on the appropriate plot

Plot was being overwritten for every other plot, every save. After that,
ran into an issue with the login prompt not properly calling back to
load images from every plot, only the one that opened the dialog.
Fix for #212 - Horizontal Resize no longer overlaps plots
Working on #237. Removed the squares from being displayed
More changes to select the nearest image
Added more accurate calculation for first-node distance
Added image selection for plots
Fixed positioning of image control, control width
Fixed bookmarks for image selection
Added dynamic y-control placement and scientific notation to prevent control from overlapping tick labels.
Fixed image set selector placement.
Add scientific notation to color legend. Changed and consolidated formatting logic across axes into new function.
Fixed infinite recursion issue with nearest image finding.
Merge branch 'tracer_model' of ssh://github/sandialabs/slycat into tracer_model

Conflicts:
	web-server/js/tracer-image-scatterplots.js
Tracked down and removed the source of the excess padding beneath grid cells.
Merge branch 'tracer_model' of https://github.com/sandialabs/slycat into tracer_model
First pass at a persistent draggable selector box.
Configurable drag threshold and better variable name.
Image control moved to x-axis, brush bound calculations centralized in SelectorBrush object, and handle adding to existing selection if ctrl key is pressed.
Fixed trans-plot brush persistence (issue #255) and tore out now unused drag handling.
Merge branch 'master' of https://github.com/sandialabs/slycat into tracer_model