New Bar widget and colour-picker for setting plot colours.

Basically what the title says. Here is a new widget, a bar-style display for feed values.
![bargraph 1](https://f.cloud.github.com/assets/1401239/2241112/cbe854b4-9cc0-11e3-862e-f8be99fd4192.png)

It's quite configurable. The position of the numeric quantity, as well as the number of graduations (if enabled) is broken out to the config window, as is colour.
![bargraph 2](https://f.cloud.github.com/assets/1401239/2241111/cbd9d63c-9cc0-11e3-9292-a56beaca18c7.png)

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This also includes the contents of my pull request https://github.com/emoncms/emoncms/pull/140, which got closed accidentally when I was cleaning up my branches (whoops). 

Description:  

Added a colour-picker for setting plot colours.

It does not work in firefox, since apparently firefox doesn't support the HTML5 colour picker yet. It does gracefully degrade to a text-box, though, so it's *usable*, just not nice and pretty. It does work in Opera and Chrome (I didn't test IE, since fuck IE).

**Edit**: [Apparently it only works in Opera/Chrome](http://caniuse.com/#search=input%20type). Hopefully the other browsers will catch up. It looks like it's slated for release in FireFox 28 (the next major release).

Anyways, the HTML5 colour picker option leverages the OS-native colour picker, so it's quite nice.

![colour picker 1](https://f.cloud.github.com/assets/1401239/2195218/a8b15ae8-9899-11e3-8e9a-ced7197d3be0.png)


![colour picker 2](https://f.cloud.github.com/assets/1401239/2195217/a5945f54-9899-11e3-937d-0d96c0fd710d.png)