Add feature change default font style and fix errors

[Thong-Tran]

Fix error in Theme picker.
Add packaging spec file for Windows, edit android spec.
Add feature: Change default font style.

from kivy.config import Config
Config.set('myapp', 'default_font_style', '<your font style>')
Config.set('myapp', 'list_fonts',
    {'<your font style>':
        # Font path, Bold, Mobile size, Desktop size (None if same as Mobile)
        ['/path/to/file.ttf', False, 14, 13]
})

[Thong-Tran]

I found some error of "Change default font style".