Added xml UI for the avfilter.scroll

data/effects/avfilter/avfilter_scroll.xml

+<!DOCTYPE kpartgui>
+<effect tag="avfilter.scroll" id="avfilter.scroll">
+	<name>Scroll</name>
+	<description>Pick median pixel from certain rectangle defined by radius.</description>
+	<author>libavfilter</author>
+	<parameter type="animated" name="av.h" min="-1" max="1" default="0" decimals="3">
+		<name>Horizontal scrolling speed</name>
+	</parameter>
+	<parameter type="animated" name="av.v" min="-1" max="1" default="0" decimals="3">
+		<name>Vertical scrolling speed</name>
+	</parameter>
+	<parameter type="animated" name="av.hpos" min="0" max="1" default="0" decimals="3">
+		<name>Initial horizontal position</name>
+	</parameter>
+	<parameter type="animated" name="av.vpos" min="0" max="1" default="0" decimals="3">
+		<name>Initial vertical position</name>
+	</parameter>
+</effect>