Add index to o_loggingtable

These 5 index speed up the course archive with a factor 1000:

create index log_target_resid_idx on o_loggingtable(targetresid);
create index log_ptarget_resid_idx on o_loggingtable(parentresid);
create index log_gptarget_resid_idx on o_loggingtable(grandparentresid);
create index log_ggptarget_resid_idx on o_loggingtable(greatgrandparentresid);
create index log_creationdate_idx on o_loggingtable(creation date);

As example setting these index on a 3GB table takes 1 minute and 1 minute 30 seconds per index and the size of the index is 500MB for the five index + primary key on MySQL.