Show humidity and location

[starryalley]

This PR contains the following:

Addition:

• Add a new configurable checkbox to show humidity along with the temperature in the menu bar.
• The current location (from OWM) will be shown in the first menu item.
• When user first launches the app the menu bar is empty. Display text message (error) in the menu bar to avoid confusion.

Greatly appreciated your work. This app has been the best lightweight weather menubar app I've seen.