Feat/palette options selection

Key Changes: 
* Changed the way links and nodes are added to the visual model. To add a node now the user must select 
the node from the palette panel and then left click on the canvas. To add a link the user must also select the link from the palette, left click on an existing node and then perform a left click on a different node.
* The attributes panel now shows a unique form for each node and link type when it is selected.
* The nodes and links now, are shown on the visual model using the visual syntax as outlined in the solution description document. 
* The people and relationship links have been removed. 
* The attributes associated with each of the links/nodes now conforms to the data models outlined in the solution description document.