Add manifest to the plugin

unl_theme/manifest.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<plugin_manifest>
+    <field key="author" value="UNL" />
+    <field key="version" value="0.1" />
+    <field key="description" value="UNL Templates Theme" />
+    <field key="website" value="http://www.unl.edu/" />
+    <field key="copyright" value="(C) University of Nebraska-Lincoln" />
+    <field key="licence" value="BSD" />
+    <field key="elgg_version" value="2009031301" />
+</plugin_manifest>
\ No newline at end of file