Added XSLTTemplate, functions that add it to transform area and documentation for that function (#144)

Co-authored-by: widlam <mikolaj.widla@gmail.com>
Reviewed-on: #144
Reviewed-by: Adam Bem <bema@noreply.example.com>
Co-authored-by: Mikolaj Widla <widlam@noreply.example.com>
Co-committed-by: Mikolaj Widla <widlam@noreply.example.com>

Frontend/assets/samples/XSLTTemplate.xslt

@@ -0,0 +1,14 @@
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+    xmlns:b="http://www.release11.com/book" xmlns:p="http://www.release11.com/person"
+    xmlns:l="http://www.release11.com/library">
+    <xsl:template match="/">
+        <Library>
+            <ReaderCount>
+                <xsl:value-of select="count(//p:person)" />
+            </ReaderCount>
+            <BookCount>
+                <xsl:value-of select="count(/l:library/l:bookList/b:book)" />
+            </BookCount>
+        </Library>
+    </xsl:template>
+</xsl:stylesheet>