Multiple panels per module

[WanWizard]

The current panel code uses the name of the module sub-directory to link to the module panel. This requires all sub-directories to end in "_panel", and also means that a module can have only one panel, given the one-to-one relationship.

The code has to be changed so that only panels of installed modules can be installed. For the panel dropdown, the module directory needs to be scanned for all php files with names ending in "_panel".

This way the module directory can have a more meaningful name. This also allows for multiple panels per module, as they will all be listed in the dropdown.

To avoid admin modules to show up here, it's is best to rename all current admin panels that now have a name ending with "_panel".

This change might have implications for the panel code in the theme engine, and possible also for the panel names used in $template and $template_vars, because panel names no longer are unique. Therefore all module needs to be modified to make sure unique names are used (include the module name?)

[WanWizard]

New feature added in rev. #1182.

All admin module names still have to be reviewed, and possibly renamed. This will be done later because all module needs to be upgraded anyway because of the change in the way we work with locales.

[WanWizard]

All modules have been checked, and changed where needed. (rev #1255)