Capped set solidity

[danielNg25]

An implementation of Capped set in solidity:
Each "element" in the set is a pair: an address and a value.
When the set gets too big (i.e., it reaches its max), it should boot out the element with the lowest
value.
Its constructor takes an argument numElements that represents the maximum number of
elements that can be in the set.

[zxstim]

Please remove all files except:

1. contracts (only the necessary contracts to make the implementation work)
2. tests
3. scripts (deployments, interactions, etc.)