Refactor connectors

[WaynePacker]

There is a lot of duplication between the Path connection and the Standard connection in the xaml Requirements:

1. Move the connectors to a new ConnectorsTemplate.xaml resource dictionary
2. Create a Template for the base connection class (AConnection.cs in base folder)
3. Create Template both the Path connection and Standard connection xaml data templates
4. Add properties to adjust color and thickness of the connection