Client: display name for nodes

[magicnat]

For each node, such as Internet Exchange, Network, host, etc. please add a new attribute to these classes, called displayName. This name will only be used in the visualization. Their internal name such as ix100 should not change. When we display a node, if a node's displayName is not empty, we will use this name to display. If it is empty, we will use the node's internal name. This way, we can give each node a meaningful name. For example, we can call an Internet Exchange "Manhattan" to represent the real "Manhattan internet exchange" in the real world.

Originally posted by @kevin-w-du in #24 (comment)

[magicnat]

Since we are implementing a new way of changing visual/display of nodes on the map, we may as well add a few other APIs too. Let's create a new class, seedemu.core.Visualization.Vertex, which have the following methods:

• setDisplayName: change the display name of a vertex. Will show on the map.
• setDescription: change description of a vertex. Will show on the upper-right details panel of the map.
• setColor / setShape / setBackgroundUrl: change color/share/background of vertex.
• setPosition: set x, y position on a vertex on map. May be useful if we want to "overlay" the topology on a real city map. Or even just load openstreetmap/google maps as background?

Elements to be shown on the map, like Network and Node, will be subclasses of Visualization.Vertex.

This may also provide some base for #24. We can create a Visualization.Layer class. Each layer can contain a different set of lists of Visualization.Vertex and Visualization.Edge, which can be created by layers like DNS. This way, layers can provide different visualization "layers" for the client.

[magicnat]

implemented setDisplayName / setDescription in fbbbc4e. Closing.