Node, Port and Custom Node Visual Enhancements

##### Changes in this pull request
- Nodes, custom nodes and input/output ports have all received their visual enhancements.

- Port and node header texts are updated to use ```Open Sans Regular``` font (instead of ```Trebuchet```).

- Unnecessary ```Grid``` panel in ```dynNodeView.xaml``` has been removed, flattening the overall node visual hierarchy.

- ```StateToColorConverter``` functionality is now extended beyond just the node fill colour to include: node header, node header text, node header border and node border colours. This way all node visual colouring is done in a centralized converter.

- ```Ports.xaml``` and ```dynNodeView.xaml``` files have been formatted to have each Xml attribute on a single line, making changes comparison much easier to read. 

- Unwanted triggers and a ```Canvas``` are removed from ```Ports.xaml```, making it leaner.

##### Updated visuals
###### The existing node, custom node, port visuals
![visual-update-before](https://cloud.githubusercontent.com/assets/5086849/2622308/602a67ee-bca5-11e3-9c25-a6b0acfb5272.png)

###### The updated node, custom node, port visuals
![visual-update-after](https://cloud.githubusercontent.com/assets/5086849/2622309/661bbb62-bca5-11e3-8fc9-2fa2940382e6.png)

##### Outstanding refactoring works
- Port height is stored in ```PortModel```, but visual positioning is all done in Xaml file. A ```PortModel``` currently has to go through hard wired calculations to obtain port centre point. If port visual is updated in Xaml file (e.g. aligning to bottom), these codes will have to be updated separately. Ideally the port center point should be derived from ```PortView``` (Xaml file) when a ```Connector``` needs to position its both ends.