Change handling of auto-generated traces in sequence diagram

[rmarx]

Currently if you only upload 1 trace, we auto-generate its opposite in the sequence diagram (e.g., you upload client, qvis generates server)

This is done by doing a full copy of the original trace and then manually swapping packet_sent for packet_received and vice versa.

This is however quite wasteful, especially for large traces, and swapping sent/received is a bit confusing for several users if they click on the squares to watch event details. Additionally, we default to showing the client-side event in the detail popup, causing the generated qlog to show up if you upload a server-side trace instead of the server-side qlog, which is even more confusing.

I did this approach initially to make it easier to re-use code across single-trace and multi-trace setups. However, adding a bit of special code for single-trace scenarios should work too.

I do have a faint recollection that this was tried initially but was too difficult for some reason, so best to do some proper analysis before starting this...