v5.1.0

Features:

• Added background image (thanks @alenas !)
• Allow customization of button icon color (thanks @klondikedragon !)
• Autofocus feature (thanks @klondikedragon !)
• Added feature to hide password-fields during signup (thanks @eggzotic !)
• Added circular loading indicator to large provider button
• Updated dependencies to be compatible with latest flutter release

Bugs fixed:

• Fixed scale transition issues.
• Added default widget size for when size lookup fails
• Fixed mounted checks in [LoginCard] (thanks @vargab95 !)