Add submenu for "New Case"

Core changes:
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1. Change New Case form to accept case type id as parameter in the URL (E.G &ctype=1)

2. Type (with case_type_id =1 ) is chosen and is read only

3. Handle post process to handle accepting case_type_id that has been passed from URL params

Extension changes(hrcase):
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In the navigation menu, add a sub-menu underneath "Cases => New Case" for each type of case using hook_civicrm_navigationMenu
Each of the above menu links will be the appended by &ctype=X (where X is the case type id)

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In the navigation menu, add a sub-menu underneath "Cases => New Case" for each type of case. (This would parallel what we do with contact subtypes.)

Two alternative ways we might implement:

1) In the HR extension, use hook_civicrm_navigationMenu to register each of the menu item.
2) In core (or in a special casemenu extension), get the list of all case types and register them in the menu.