pySim-shell: Use argparser for verify_adm to support --help

Let's add a proper argparser instance for the 'verify_adm' command,
avoiding situations where the user types 'verif_adm --help' and then
--help is interpreted as the PIN value, removing one more attempt from
the failed ADM1 counter.

Let's use that opportunity to improve the documentation of the command.

Change-Id: I3321fae66a11efd00c53b66c7890fce84796e658

docs/shell.rst

@@ -137,10 +137,11 @@ Example:
 
 verify_adm
 ~~~~~~~~~~
-Verify the ADM (Administrator) PIN specified as argument.  This is typically needed in order
-to get write/update permissions to most of the files on SIM cards.
 
-Currently only ADM1 is supported.
+.. argparse::
+   :module: pySim-shell
+   :func: PySimCommands.verify_adm_parser
+
 
 Example (successful):
 ::