Ticket #473: Add option of saving User ID in xml

Changes Made:
1. Choose if User ID is to be saved during import of divelogs from
   subsurface webservice. Save function must be called once for change
   to take effect.
2. Dialogbox retains the last set option or as per present xml.
3. Suitable modifications made in parse-xml.c
3. bool save_userid_xml depends on presence/absence of userid in xml

Todo:
1. Force save once on clicking accept ?

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>