Animation settings added

[selmaVH1]

fixes #7491
Animation settings added to symbol_selector and vector_properties.

[DelazJ]

Suggested change

	To allow any symbol to become an animated symbol, you can utilize
	To allow any symbol to become an :ref:`animated symbol <animated_marker>`, you can utilize

Let's connect sections; the pr build will fail but just a temporary issue

[DelazJ]

Let's be more generic in the index

Suggested change

	.. index:: Animation Settings
	.. index:: Animation

[DelazJ]

Let's clearly show the steps people should follow

Suggested change

	Start by going to the :guilabel:`Advanced` menu, within this menu you will
	find the :guilabel:`Animation settings` option. Select
	|checkbox| :guilabel:`Is Animated` and you will activate animation for
	the symbol. Once animation is activated you can use expressions to control
	symbol properties. For example, setting the symbol's rotation to the data
	defined expression ``@symbol_frame % 369`` will cause the symbol to rotate
	over time, with rotation speed dictated by the symbol's frame rate.
	#. Start by going to the top symbol level and select :guilabel:`Advanced` menu in the bottom right of the dialog
	#. Find the :guilabel:`Animation settings` option
	#. Check |checkbox| :guilabel:`Is Animated` to enable animation for the symbol
	#. Configure the :guilabel:`Frame rate`, i.e. how fast the animation would be played
	#. You can now use the ``@symbol_frame`` variable in any sub-symbol data defined property
	in order to animate that property.
	For example, setting the symbol's rotation to the data
	defined expression ``@symbol_frame % 360``
	will cause the symbol to rotate over time, with rotation speed dictated by the symbol's frame rate.

I wonder if the last paragraph should instead be used as caption for a (welcomed) animation showing how to use that feature.