MYOB Integration tweaks

• Detect if MYOB supplier that c9 maps to has been deleted; if so then request user to remap any c9 suppliers during sync
• Configuration option to skip syncing a certain c9 suppliers. Setting is memorized only for the duration of the sync operation. Next sync user has to map the supplier and skip it again.  Note that skipped invoices are not flagged as synced, so if you run sync again, c9 will try to resync prior skipped invoices.
• Configure mapping, include option to refresh list of MYOB suppliers and account lists.  Useful when you go to map a supplier and find that card is missing in MYOB. You can switch to MYOB, add the card, switch back to c9 click refresh and see the newly added card
• Bugfix : under some circumstances during configuration of MYOB, c9 would crash. (Caused by incorrect database access)