Have different mention types invoke different embeds

[violine1101]

As mentioned in #11, it might be nice to have the option to invoke a different mention type depending on how you mention it. For instance, when mentioning a ticket using its URL, the mention would only be very minimal, similar to how EigenBot does it. Similarily, there could be a "medium" and "very detailed" mention type, which each could be invoked in different ways, e.g. by using >MC-12345 or !MC-12345.