IVGCVSW-5213 Switch armnnConverter over to cxxopts
IVGCVSW-5213 Switch armnnConverter over to cxxopts

* Swap out boost::program_options  with cxxopts.
* Remove const from argv declaration to conform to cxxopts.
* Clean up CLI handling around multiple inputs and shapes.
  Each input must be specified with its own -i param.
  Each corresponding -s parameter must be specified too.

Signed-off-by: Colm Donelan <f9860052b68289c6785c07724a8e72ee77c1bf0a@arm.com>
Change-Id: I01c2683dbca51b2322c98913731ac82a59e400a5

ARM-software/armnn,ARM-software/armnn,ARM-software/armnn