making plugin assets in automake mode
added twig filter css

this filter can be used to convert an associative
array such as array("width" => "50%") into a css
string such as "width:50%;".
added empty option for optional axes

users needed to be able to manually select
columns for optional axes, and to deselect
them at any point. hence we needed an option
representing "no selection".
html selects don't support html content
proper control markup / support styling
no session needed in plugin install script
removed css, added inline mode

the inline mode allows vis options to go into the
same row by assigning display: inline-block; to the
outer vis-option-group element
coloring circles, too
dataset.list returns a plain objects

a list of simple plain objects is sometimes
simpler to handle than operating with datasets
default column API.
updated d3-light

this adds d3.scale.sqrt()
build assets