Refactor state save/load

- Fix bug where new install was relying on the migration to run on
startup to fix up the default config
- Moved save/load functions into state.js
- Removed exported getInitialState, getDefaultSavedState since that's
leaky. The state module should take care of that.

main/windows/about.js

@@ -31,7 +31,7 @@ function init () {
   // No menu on the About window
   win.setMenu(null)
 
-  win.webContents.on('did-finish-load', function () {
+  win.webContents.once('did-finish-load', function () {
     win.show()
   })