Collapse invites into joins and parts more efficiently

[ara4n]

See #74. @lukebarnard1 implemented collapsing joins/parts, but it could take up less room:

• The collapsed view should be entirely replaced when expanded, rather than the expansion being added to the collapsed summary
• Invites should be included as well as joins/parts in the collapsing, otherwise every time an IRC user joins, they are first invited by the bridge and so break the collapsing.

[lukebarnard1]

The collapsed view should be entirely replaced when expanded, rather than the expansion being added to the collapsed summary

@ara4n: does this mean it should not be toggle-able?

Invites should be included as well as joins/parts in the collapsing, otherwise every time an IRC user joins, they are first invited by the bridge and so break the collapsing.

Should the invites be included in the summary? E.g. "12256 people were invited"

Also, I think we could fix #2594 at the same time by handling all kinds of member events. How do we feel about "123 people were banned/kicked/invited" being included?

Discussion about ordering/causality problem: #2856 (comment)

[ara4n]

We should still be able to expand/collapse; let's just put the toggle at the end of the topmost message (whether it is expanded or collapsed).

Yes, let's include invites too. So the categories end up being joined/left/kicked/banned/invited, ordered chronologically as per #2856