Implements dashed lines

Adds support for dashed lines (#514) using jquery.flot.dashes.js, although, as mentioned on these two links
 
* https://code.google.com/p/flot/issues/detail?id=61
* http://stackoverflow.com/questions/24593077/does-jquery-flot-dashes-js-support-plothover-and-plotclick

I had to change a line in `jquery.flot.js` to be able to get the crosshair on the dotted lines. This is a first try at it and I must admit I never really touched Angular before, please therefore tell me what to change and I will do what I can.

Also, the `dashes` object gets the same linewidth as the global linewidth, these are two different plugins but I strongly feel that the user should not have a "Dashed line width" and a "Line width" selector side by side. Setting `dashes.show` to true also sets `lines.show` to be able to see the dashed line.

Screenshots below

![screenshot on 2014-10-15 at 02-59-38](https://cloud.githubusercontent.com/assets/937179/4637406/2cb83740-53ec-11e4-957c-ad0b2eeaaffe.png)
![screenshot on 2014-10-15 at 02-59-49](https://cloud.githubusercontent.com/assets/937179/4637411/335330b4-53ec-11e4-9e85-c21d95b40bbd.png)