Add a !projects command

It should print the list of gitlab/github/bitbucket repositories that we manage. It could work the same way !ping does printing the list in a private message so we don't spam the channel.

Example:

!projects
novawebdevelopment.com website: https://github.com/novawebdevelopment/Website
nea4or website: https://github.com/jelkner/nea4or
nea4or members ams: https://gitlab.com/novawebdevelopment/nea4or_ams
elizabeth guzman wesite: https://bitbucket.org/novawebdevelopment/pwpc
...

We'll also need an option for channel operators to maintain the list (add/remove links) and a !help command describing how to use it.