#2 Installation of triggers

[prugniel]

The update_meandata trigger definition is in the files
leda_sql/src/droptrig.sql and trigger.sql

These scripts are executed when something is changed in
leda_sql.

Important bug: The triggers are not installed when we
restore the db from a dump, or at the first installation.

Other issue (minor): It would be good to separate the
triggers from leda_sql (we should not reinstall
leda_sql if we modify a trigger).

Solving this bug is required before we can install a
'test' version (ledadev) of the database.