UserInputBlock: prepare reusable sections for UserInput dialogs

UserInputBlock allows to build a section for a UserInput dialog.

It is referenced by name, and contains valid children of UserInput like Variables, Events, and LoadUserInputBlock.

If/Else sections are also available.

It cannot be used to replace direct UserInput parameters like Title, ButtonTextOk etc.

If two blocks are defined with the same name, the second block replaces the first block, which is permanently eliminated.

Variables used inside the block are interpreted at run time.

Tag Attributes

	<userinputBlock Name="Block2">
		<Variable Type='label' name='label21' label='BLOCK 21'/>
		<Variable Type='label' name='label22' label='BLOCK 22'/>
		<If target="var" test="{%v_Switch%}" mode="Equals" Value="2">
			<Variable Type='label' name='ifinblock' label='FROM IF IN BLOCK'/>
		</If>
	</userinputBlock>