Add php5-ldap for LDAP authorization

Dockerfile

@@ -18,7 +18,7 @@ ENV LAST_REFRESHED 6. September 2015
 RUN DEBIAN_FRONTEND=noninteractive \
     apt-get update && \
     apt-get -y upgrade && \
-    apt-get -y install wget lighttpd php5-cgi php5-gd && \
+    apt-get -y install wget lighttpd php5-cgi php5-gd php5-ldap && \
     apt-get clean autoclean && \
     apt-get autoremove && \
     rm -rf /var/lib/{apt,dpkg,cache,log}