Category browser with AJAX distant-parent support

This will be a new module, called categoryi_browser, which will essentially be a full port of the taxonomy_browser module to the category system. However, if users only need the features of taxonomy_browser, then they can simply use this module through the taxonomy wrapperi.

As well as the features of taxonomy_browser, category_browser will support categories that have distant parentiis. Users will be able to select a category from one list (representing one containeri), and the categories in another list (representing another container) will be re-populated to show only the children of the selected category. This re-populating will be done without reloading the page, using AJAX. If AJAX support is not available, the feature will degrade by simply populating all lists with all categories.

Working out which lists contain categories with distant children will not be up to the module. The site administrator will be able to configure this through the module's settings page. However, working out which lists contain categories with distant parents will be up to the module.