Added List Certificate Function

[psgoundar]

This is a list function that show all the issues Certificates from the /etc/openvpn/easy-rsa/pki/index.txt file and formats it into a table to show the Status, Name and Expiration Dates.

[randshell]

Fixes #563

[randshell]

At the moment index.txt contains revoked users too so this function will show them #566

[psgoundar]

For my personal Use case I need to list revoked users as well to see them. But I can see why that would not be needed. I can take remove all revoked users or potentially in a future update add another submenu to list All or only valid Certificates?

[randshell]

@psgoundar I'd like to see revoked users too but there are some user who asked to not show them #566 (comment).

My previous comment was to link to the issue not to request changes, @angristan will decide on this.

[angristan]

3, 8, 9?

[psgoundar]

I've got multiple other options that I've added to my repo And I was planning on slowly submitting all the changes up to the main repo.
And I didn't want to continually be renumbering the remove and Exit options
Such as:
echo " 1) Add a new user"
echo " 2) Revoke existing user"
echo " 3) List Current Issued Certificates"
echo " 4) List Current Active Users"
echo " 5) Backup Configuration"
echo " 6) Restore Configuration from Backup *Incomplete"
echo " 7) Sync Configuration to Alternate Servers *Incomplete"
echo " 8) Remove OpenVPN"
echo " 9) Exit"

[angristan]

Please do the appropriate changes for this PR :)

[psgoundar]

I think I totally Screwed up my branch. I will close this pull Request. And pull another with the neccessary Changes.

[angristan]

Ok :)

[psgoundar]

Repulled Main Repo and Redoing changes