Slack slash-command for listing skills

[rthbound]

Create a slash command, e.g. /listskills, that will list the distinct skills associated with users. I don't think it should return all skills, rather only return those skills that have been added to users.

Something like Skill.joins(:users).distinct.order(:name)

[rmd6502]

add Skill.joins(:projects), so users looking for a project to join can know what's being looked for overall