Stroke dasharray

Adds support for stroke-dasharray attribute on shapes. I've also added a test SVG file and added it to the demo app.

In addition, the SVG spec specifies that stroke-dasharray might be white space delimited, but the current code smushes the values together, so stroke-dasharray="4 2 8 7" would become one value, 4287. 9d644b0 fixes this issue, and is applied in a separate commit in case it should not be included for some reason. 

I did notice that the test file "London_European_nation_states.svg" defines some `stroke-dasharray`s, but does not appear to render them. It looks like it also defines many `stroke-dasharray:none;`, and cascadedValueForStylableProperty:@"stroke-dasharray" never returns a value other than 'none', so my  hunch is it is still rendering correctly, and the input SVG is not clean.