Refactor karma config

- rename test:multi npm target to test-multi, for consistency with react-sdk
- base karma webpack config on the distribution one
- include Olm if we have it
- don't use the karma source loader - it's pointless given we webpack
  everything.
- turn off module listing in the webpack stats to shorten the console output

package.json

@@ -46,7 +46,7 @@
     "clean": "rimraf lib webapp electron/dist",
     "prepublish": "npm run build:compile",
     "test": "karma start --single-run=true --autoWatch=false --browsers PhantomJS --colors=false",
-    "test:multi": "karma start"
+    "test-multi": "karma start"
   },
   "dependencies": {
     "babel-polyfill": "^6.5.0",
@@ -111,7 +111,6 @@
     "karma-junit-reporter": "^0.4.1",
     "karma-mocha": "^0.2.2",
     "karma-phantomjs-launcher": "^1.0.0",
-    "karma-sourcemap-loader": "^0.3.7",
     "karma-webpack": "^1.7.0",
     "minimist": "^1.2.0",
     "mkdirp": "^0.5.1",