Add GUI icon to indicate elytra toggle status

[bendvis]

Thanks for this great little mod! It's saving my sanity in a modded world where I have both a jetpack and elytra equipped. Thought I'd add a little indicator on the HUD for whether the elytra are toggled on or off.

• Core functionality remains unchanged
• Add icons for enabled and disabled flight status
• Display the appropriate icon next to the hotbar by default
• Add configs to hide the icon when flight is enabled or disabled
• Add config to customize position of the icon
• Bump version number to 1.1, remove unused reference to Caelus