Clean up npm package (#904)

* ignore everything but official contracts for npm

* add tests to npm package

* remove truffle migrations stuff

* remove seemingly unused npm dependency

* clean up dependencies

contracts/.npmignore

@@ -0,0 +1,2 @@
+mocks
+examples

contracts/lifecycle/Migrations.sol

@@ -1,21 +0,0 @@
-pragma solidity ^0.4.21;
-
-import "../ownership/Ownable.sol";
-
-
-/**
- * @title Migrations
- * @dev This is a truffle contract, needed for truffle integration, not meant for use by Zeppelin users.
- */
-contract Migrations is Ownable {
-  uint256 public lastCompletedMigration;
-
-  function setCompleted(uint256 completed) onlyOwner public {
-    lastCompletedMigration = completed;
-  }
-
-  function upgrade(address newAddress) onlyOwner public {
-    Migrations upgraded = Migrations(newAddress);
-    upgraded.setCompleted(lastCompletedMigration);
-  }
-}