Resolve "LDAP connector"

This merge request allows to configure smasch in a way that authentication is done via LDAP.

However, due to the fact that data stored in smasch is very sensitive, LDAP authentication is supported only for users that already exist in smasch (they will not be created automatically). Moreover worker flag ldap_user must be set to True.

To configure ldap there are two parameters that must be added to local_settings.py:

AUTH_LDAP_SERVER_URI = "ldap://lcsb-cdc-lums-01.uni.lu"
AUTH_LDAP_BASE_DN = "cn=users,cn=accounts,dc=uni,dc=lu"

By default LDAP connection is disabled.

Closes #380 (closed)

debian-template/control

@@ -11,7 +11,7 @@ Vcs-Browser: https://git-r3lab.uni.lu/NCER-PD/scheduling-system.git
 Package: smasch
 Architecture: all
 Section: science
-Depends: ${misc:Depends}, python3(>=3.6), virtualenv, libcurl4-gnutls-dev, libpng-dev, libfreetype6-dev, libpq-dev, gcc, g++, python3-dev, libgnutls28-dev, libjpeg-dev, libfreetype6-dev, pkg-config, cron, libsasl2-dev, python-dev, libldap2-dev, libssl-dev
+Depends: ${misc:Depends}, python3(>=3.6), virtualenv, libcurl4-gnutls-dev, libpng-dev, libfreetype6-dev, libpq-dev, gcc, g++, python3-dev, libgnutls28-dev, libjpeg-dev, libfreetype6-dev, pkg-config, cron, libsasl2-dev, libldap2-dev, libssl-dev
 
 Description: SMart SCHeduling - research study scheduling program
  The program controls and simplifies the scheduling, and is able to manage a