[Fix #4732] Add required to menu item type

Fix for #4732 . Add required attribute

## Original Report

#### Steps to reproduce the issue
1. Go to Menu->Main Menu-> Add New Menu Item.
2. Open Add New Menu Item form.
3. Fill the data only in title field and save the record.
4. Record is saved successfully.

#### Expected result
If mandatory field(Menu Item Type) is kept blank then record should not save. Also it should give proper validation message.


#### Actual result
Record saved successfully without any validation message.![screen shot 2014-10-17 at 02 37 12](http://issues.joomla.org/uploads/1/9adc1d4e46a62edc0933ac6ed37e2cd8.jpg)


#### System information (as much as possible)



#### Additional comments