Added xml UI for the avfilter.colorcontrast

data/effects/avfilter/avfilter_colorcontrast.xml

+<!DOCTYPE kpartgui>
+<effect tag="avfilter.colorcontrast" id="avfilter.colorcontrast">
+	<name>Color Contrast</name>
+	<description>Adjust color contrast between RGB components.</description>
+	<author>libavfilter</author>
+	<parameter type="animated" name="av.rc" default="0" min="-1" max="1" decimals="3">
+                <name>Red-Cyan contrast</name>
+        </parameter>
+        <parameter type="animated" name="av.gm" default="0" min="-1" max="1" decimals="3">
+                <name>Green-Magenta contrast</name>
+        </parameter>
+        <parameter type="animated" name="av.by" default="0" min="-1" max="1" decimals="3">
+                <name>Blue-Yellow contrast</name>
+        </parameter>
+        <parameter type="animated" name="av.rcw" default="0" min="0" max="1" decimals="3">
+                <name>Red-Cyan weight</name>
+        </parameter>
+        <parameter type="animated" name="av.gmw" default="0" min="0" max="1" decimals="3">
+                <name>Green-Magenta weight</name>
+        </parameter>
+        <parameter type="animated" name="av.byw" default="0" min="0" max="1" decimals="3">
+                <name>Blue-Yellow weight</name>
+        </parameter>
+        <parameter type="animated" name="av.pl" default="0" min="0" max="1" decimals="3">
+                <name>Preserving lightness</name>
+        </parameter>
+</effect>