Make EBE Compatible with 'Single Widget' Selector Plugin

Currently, the module iterates over the "#tab_selector" form element of an entity browser form in search of widgets that have 'multiselect' configured as their enhancer. This makes the module incompatible with entity browsers that are configured to use the 'Single Widget' option, rather than the 'Tabs' option, even if their single widget does in fact have an enhancer configured.

This patch modifies the logic to retrieve widget information from the entity browser config, which includes all widgets in use by that browser. Thus, enhancer libraries will be attached regardless of what widget selector option is in use.