Fleasy 0.3.0

• Add Flashbar extensions to BuildContext
  • showSuccessFlashbar(...)
  • showInfoFlashbar(...)
  • showErrorFlashbar(...)
  • showNoConnectionFlashbar(...)
• Add addHtpps to string extensions
• BREAKING: Refactor EasyFutureBuilder & EasyStreamBuilder:
  • errorIcon & isEmptyIcon now take IconData instead of FaIcon
  • new attributes: textStyle & iconStyle
• BREAKING: Remove shortestScreenSide & longestScreenSide
• Improve README