Fixes #21 and fixes #22; cleaned up bar width and series spacing logic when adding additional bar chart series
Fixed #19; removed type property from axis object; scale types now chosen exclusively from chart type
Fixes #16; needed to use remainingVariables in PICK_CONTROL as had already been used in ADD_CONTROL
Fixes #20 - when a user switches the x-axis to a quantitative variable, by default show them the scatterplot... switching other axes won't trigger this
Fixes #18 - x-axis ordinal or quantitative number of ticks depends on width of screen; adjusted tick label format to include SI prefixes
Merge branch 'wip-cntd-barchart' of https://github.com/jaericson/3x

(Pull Request #23)