first iteration of LDAP support

basic copying of users from LDAP to MongoDB on authentication works
currently only plain-text passwords are support from LDAP
if LDAP is turned off the current implementation still allows those users to authenticate, this will be fixed in the next iteration.

issue Graylog2/graylog2-web-interface#266
first part of widgets #360
Merge git://github.com/Graylog2/graylog2-web-interface into develop