Refactor API: s/node/vertex

[lintool]

We should rename Node to Vertex in the API. Two main reasons:

1. Vertex makes you sound smarter... :)
2. If we want to start playing with partitioning, we want to reserve "Node" for logical/physical machine nodes, so getNode and getVertex can be easily disambiguated.

[pankajgupta]

Agreed.

[lintool]

Okay, I'll refactor and send a pull request... this will help me get my feet wet and learn the API, etc.

[pankajgupta]

Looking forward :)