add BreakPointManager to index.js

remix-core/index.js

 var CodeManager = require('./src/code/codeManager')
+var BreakpointManager = require('./src/code/breakpointManager')
 var StorageViewer = require('./src/storage/storageViewer')
 var StorageResolver = require('./src/storage/storageResolver')
 var TraceManager = require('./src/trace/traceManager')
@@ -8,7 +9,8 @@ module.exports = {
     web3: null
   },
   code: {
-    CodeManager: CodeManager
+    CodeManager: CodeManager,
+    BreakpointManager: BreakpointManager
   },
   storage: {
     StorageViewer: StorageViewer,