Improve OS menu (#1563)

* Remove reload options, new file/help menus, tools/log at bottom

* Further menus refactor: install handlers at template creation

* WIP: Further tune menus, add custom about window

* New About window, new help menu items, menu labels now i18n

* Default device name on registration is now computer hostname

The OS of the device makes sense for those of us testing across a lot of
different OSes. And maybe for a user with just one desktop device. But
most users with multiple desktop devices are using the same OS for both.

* About window: Only show window when content is ready

* Fix typo in app/menu.js

js/views/inbox_view.js

@@ -147,7 +147,6 @@
             welcomeToSignal         : i18n('welcomeToSignal'),
             selectAContact          : i18n('selectAContact'),
             searchForPeopleOrGroups : i18n('searchForPeopleOrGroups'),
-            submitDebugLog          : i18n('submitDebugLog'),
             settings                : i18n('settings'),
             restartSignal           : i18n('restartSignal'),
         },