Remove the shoppergroups plugin, which was never finished/properly implemented. Its functionality is provided by custom variables, anyway

V4.0.2: Old php versions do not support using array elements directly for function calls. We need to use call_user_func_array instead, otherwise we get an error "Function name must be a string"...

V4.0.1: Add onVmOrdernumberPostprocessNumber trigger to postprocess the numbers, e.g. to append a checksum or store the number in some external system, too

V3.4: Fix JS call with string arg; Fix SQL update script, which so far erased the invoice number counters

V3.2: Fix stupid typo that broke all counter editing (counter type was changed from int to string, so extracting AJAX args needed to request strings, too

Some last bug fixes

Add plugin framework for custom variables: trigger onVmOrdernumberGetVariables(&$reps, $fmt, $nrtype, $details)

-) Implement loading indicator during the AJAX calls
-) Give each type of number its own fieldset (and thus its own
   tab in the plugin config)
-) Fix display of system messages generated by ajax call in Joomla 2.x
-) Fix JSON output in Joomla 2.x (two Content-Disposition
   headers generated, which broke parsing of the AJAX response
   in Chromium) -> Use raw format for joomla and manually send
   the json content-disposition header
-) Fix jQuery in Joomla 2.x

Implement counter editing in the plugin config; Some minor issues are left, the functionality is fully implemented