Re-enable solidity coverage

- Upgrade version
- Re-enable in travis.yml
- Move mocks to contracts folder for instrumentation

contracts/mocks/PausableMock.sol

@@ -0,0 +1,25 @@
+pragma solidity ^0.4.18;
+
+
+import '../lifecycle/Pausable.sol';
+
+
+// mock class using Pausable
+contract PausableMock is Pausable {
+  bool public drasticMeasureTaken;
+  uint256 public count;
+
+  function PausableMock() public {
+    drasticMeasureTaken = false;
+    count = 0;
+  }
+
+  function normalProcess() external whenNotPaused {
+    count++;
+  }
+
+  function drasticMeasure() external whenPaused {
+    drasticMeasureTaken = true;
+  }
+
+}