#85 Query Builder: check for PK when saving join to file

[PAscal]

When saving a join that has been manually added (join name is NULL)
tab1.fieldx -- tab2.fieldy
take care to save FK field and PK field in the correct order in csv file
by asking if tab1.fieldx belongs to PK ?
if YES tab1.fieldx is PK, tab2.fieldy is FK
if NO tab1.fieldx is FK, tab2.fieldy is PK
...