pre-commit-hook: Added checks for multi-level template parameters and 'NULL'

Patch contributed by Bruno Santos
Resolves bug-report http://bugs.openfoam.org/view.php?id=2267

   1. Spaced ending of multi-level template parameters are not allowed, such as:

       List<List<scalar> >

     which instead should be:

       List<List<scalar>>

   2. The use of the 'NULL' macro should be replaced by 'nullptr'