[Feature Request] Multi clients management

I suggest several modifications to easily manage
systems with a lot of clients.
```
$ $SCRIPT_NAME client list # Table for example

Name Status Expiry Remaining
---- ------ ------ ---------
User1 Valid 2036-08-16 3649 days
User2 Valid 2036-08-16 3649 days
User3 Valid 2036-08-16 3649 days
NewUser Valid 2036-08-16 3649 days
UserToRevoke Valid 2036-08-16 3649 days
```
1) Revoke several clients with wildcards
```
$SCRIPT_NAME client revoke User1 User2 # revokes user1, user2
$SCRIPT_NAME client revoke User* # revokes user1-3, UserToRevoke
$SCRIPT_NAME client revoke User? # revokes user1-3
$SCRIPT_NAME client revoke User[123] # revokes user1-3
```
2) Add several clients
```
$SCRIPT_NAME client add newUser1 newUser2 # adds two new users
$SCRIPT_NAME client add newUser1 newUser2 --password 1234 # adds users with the same password
$SCRIPT_NAME client add newUser1 newUser2 --cert-days 20 # adds users with the same certification days
```
3) List with filters
```
$SCRIPT_NAME client list # Lists only valid clients (default='valid')
$SCRIPT_NAME client list --valid # The same
$SCRIPT_NAME client list --revoked # Lists only revoked clients
$SCRIPT_NAME client list --all # Lists both revoked and valid clients
```

These ones are ready to review, there is something we want implement
in the future:
1) List with users name pattern and wildcards
2) Renew several clients with wildcards