graph component: add lineWidth attribute

Also change attribute name in grapher from strokeWidth
to lineWidth and implement drawing with lineWidth.
graph component: support optional xProperty attribute

The default value for xProperty is 'time' and this
is what will the X axis is assigned to by default.

You can now optionally set xProperty to another property
to make an X-Y scatter-plot graph.

To draw dots instead of lines set the 'lines' attribute to false.
grapher: speed up drawing of dots

Using arc method is quite slow, replaced with fillRect.
latent heat: add bar graphs and Temp/Energy scatter graph