Improvements to multi-input control

Here are several improvements and fixes I've recently made:

• ability to define "default" field value, which is used to reset field after adding/editing/cancel editing of record;
• ability to support "radio" type fields;
• ability to define unlimited number of filed properties in object-style notation (not set of parameters as before);
• ability to change any properties (except name of course) of registered in control fields in real-time (e.g. default value);
• "change" javascript event is called when value is changed automatically (not by user);
• ability to make individual records in control read-only (no editing/delete possible);
• "escape" function replaced with "encodeURIComponent", since it provides proper ending of "non-english" letters;
• in case if multiple fields in form contains an error, then all errors are shown as single "alert", not multiple ones as before;
• error about empty required fields are now shown using same style as other errors (with error field list);
• field name wasn't displayed in error message in case if "error_field" option was using in field declaration (in unit config);
• OnBeforeItemCreate/OnBeforeItemUpdate events were not called during ajax field value validation;
• Parameter "is_last" wasn't available in PredefinedOptions tag, making it impossible to list options as javascript object;