[FIX] include account token position when describing exports

[brianmcgee]

Addresses part of #597

When describing exports without any account token positions, the output looks like this:

+------------------------------------------------------------------------------------------------------------+
|                                                  Exports                                                   |
+--------------+-------------------+--------------+------------------------+--------+-------------+----------+
| Name         | Type              | Subject      | Account Token Position | Public | Revocations | Tracking |
+--------------+-------------------+--------------+------------------------+--------+-------------+----------+
| binary-cache | Service [Chunked] | nits.cache.> | -                      | No     | 0           | -        |
+--------------+-------------------+--------------+------------------------+--------+-------------+----------+

When describing exports that do contain account token positions, the output looks like this:

+----------------------------------------------------------------------------------------------------------------------------------+
|                                                             Exports                                                              |
+-----------------------------+------------------+----------------------+------------------------+--------+-------------+----------+
| Name                        | Type             | Subject              | Account Token Position | Public | Revocations | Tracking |
+-----------------------------+------------------+----------------------+------------------------+--------+-------------+----------+
| account-monitoring-streams  | Stream           | $SYS.ACCOUNT.*.>     | 3                      | Yes    | 0           | N/A      |
| account-monitoring-services | Service [Stream] | $SYS.REQ.ACCOUNT.*.* | 4                      | Yes    | 0           | -        |
+-----------------------------+------------------+----------------------+------------------------+--------+-------------+----------+

[aricart]

LGTM