Hide missing time-scatter data
Allow redraw of histogram charts

Fixes histogram charts not redrawing on UI interaction
after updates to the ChartingController logic in
commit 7fbcf31
Merge pull request #73 from CloudNiner/feature/chart-redraw-option

Allow redraw of histogram charts
Add logic for fading data in and out
Merge pull request #74 from azavea/feature/handleMissingTimeScatter

Feature/handle missing time scatter