Add a global shortcut to open DevTools

Fixes: https://github.com/resin-io/herostratus/issues/33

appveyor.yml

@@ -19,7 +19,6 @@ install:
   - ps: Install-Product node $env:nodejs_version x64
   - npm -g install npm@2
   - set PATH=%APPDATA%\npm;%PATH%
-  - npm install -g electron-prebuilt
   - npm install
 
 build: off

lib/herostratus.js

@@ -21,6 +21,7 @@
  * THE SOFTWARE.
  */
 
+var globalShortcut = require('global-shortcut');
 var path = require('path');
 var app = require('app');
 var Menu = require('menu');
@@ -49,6 +50,10 @@ app.on('ready', function() {
       icon: path.join(__dirname, '..', 'assets', 'icon.png')
     });
 
+    globalShortcut.register('CmdOrCtrl+Alt+I', function() {
+      mainWindow.openDevTools();
+    });
+
     mainWindow.showUrl(path.join(__dirname, 'index.html'));
   });
 });