Themes should have "inherit" field, not theme properties

[mrshiposha]

According to the RMRK spec only a theme can inherit another theme.

But at the moment theme properties have an inherit field.

rmrk-substrate/traits/src/theme.rs

Lines 6 to 24 in 078d7c9

	#[cfg_attr(feature = "std", derive(Eq))]
	#[derive(Encode, Decode, RuntimeDebug, TypeInfo, Clone, PartialEq)]
	pub struct Theme<BoundedString> {
	/// Name of the theme
	pub name: BoundedString,
	/// Theme properties
	pub properties: Vec<ThemeProperty<BoundedString>>,
	}
	#[cfg_attr(feature = "std", derive(Eq))]
	#[derive(Encode, Decode, RuntimeDebug, TypeInfo, Clone, PartialEq)]
	pub struct ThemeProperty<BoundedString> {
	/// Key of the property
	pub key: BoundedString,
	/// Value of the property
	pub value: BoundedString,
	/// Inheritability
	pub inherit: Option<bool>,
	}

Also, I can't see where the inheritance info is stored in the Pallet.