Bug 16454: Use 'inventory' instead of 'inventory/stocktaking'

Bug 16454: Use 'inventory' instead of 'inventory/stocktaking'

To test:
1) Go to the tools home page. Confirm it says 'Inventory' instead of
   'Inventory/stocktaking' in heading and in description
2) Click Inventory. Confirm heading now says 'Inventory' instead of
   'Inventory/stocktaking'
3) Confirm that it now says 'Inventory' instead of
   'Inventory/stocktaking' in the tools menu along the left of the page
4) Click Help in top right corner. Confirm help heading now says
   'Inventory' instead of 'Inventory/stocktaking'
5) Go to user account page, go to Set Permissions
6) Expand Tools option and confirm it says 'inventory' instead of
   'inventory (stocktaking)'

Sponsored-by: Catalyst IT
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>