Fix for issue 3686 (makeldif does not parse redirect to file based attribute)

The fix for the issue consists basically in two parts.

1. Update the parser in the class TemplateFile to handle correctly the attributes referring to an URL (like usercertificate:< file:///mycertificate) and base64 attributes (usercertificate:: <base64 value>).

2. Update the class TemplateEntry to get the LDIF representation of the entry.  The interfaces in Branch, LDIFWriter, MakeLDIFInputStream and EntryWriter have also been updated to handle TemplateEntry.