OPENDJ-1490 (CR-3724) Replicated server fails to start after upgrade due to missing ReplicationBackend class

Added upgrade tasks for:
- Removing 'dc=replicationchanges' backend
- Removing ACI for 'dc=replicationchanges'


Upgrade.java:
Registered upgrade tasks.

UpgradeTasks.java:
Added deleteConfigEntry().
Factorized code by extracting method perform0().
Fixed javadocs.

UpgradeUtils.java:
In updateConfigFile(), renamed lines parameter to ldifLines + changed String dn local variable to DN ldifDN + added support for deleting entries.

tools.properties:
Added messages for upgrade tasks.
Fixed typos.


admin_tool.properties:
Fixed typos.

SaltedMD5PasswordStorageSchemeTestCase.java:
Removed unused import.