Save, Load And More!

Added

• Feature to save and load the whole whiteboard as a .rainbow file.
• Settings page with multiple settings.
• New Themes:
  • Dark Whiteboard: Dark UI, White board.
  • Light Blackboard: Dark UI, Black board.
• New Settings:
  • "Start Maximized": Start the app maximized.
  • "Start Fullscreen": Start the app fullscreen.
  • "Show Menu Bar When Fullscreen": Show the menu bar in fullscreen mode.
• New shortcut to switch to the previous tool (#14)
• .msi installer and .zip for windows.

Changed

• UI clean up, redesign.
• Try to follow GNOME Human Interface Guidelines
• Use Font Awesome v5 icons.
• The brush and line color are displayed under the tool button.
• Many smaller tweaks

Fixed

• #13