Create a cpp helper class to calculate the correct delegate width given it's parent width.
This is designed to be more robust and hopefully easier to understand than the current mass of javascript calcs.
BUG: 470167
Limit the maximum number of avatars shown for other user read markers and collapsed state events
For state events \

For read markers \

- Update the message event and user models so that the full source url is output.
- Separate the reply author into its own role
- Create an empty user object that can be passed so that the QML code no longer needs to check if certain parameters exist.
- Make avatarForMember return and empty QUrl if a valid avatar cannot be found and make use in the user and event models
As well as cleaning up the QML this should also stop the QML Image: Media id '' doesn't follow server/mediaId pattern spam in the log.
Implement folding sections for multiple consecutive state events. This also reworks some of the aggregated text output:
- Only new days cause a new section
- The aggregated text starts with either a single username or n users
- If the same user did the same action mutltiple times it will be in the aggregated text a user did x n times
- When there are multiple authors in a block with multiple state event types it will use or rather than and before the last event. e.g 3 user left the room or joined the room.
Folded

Unfolded

Implements network/neochat#90
**Updated**
Add a section label at the top which shows the date label of the next section up. This means that the user will always be able to see the date of all messages on screen.

From the feedback given I've added a background at the top. I also added an underline to the heading which applies both at the top and in the listView since they use the same component. I added it originally for the top because I felt it looked a bit weird having messages appear from behind a heading background the same colour as the listView background.
Note: I know the gaps between messages are not right. I had to set the spacing in the listView to 0 to prevent itemAt returning null. I plan to add it back in as part of the delegate code before it would be merge.
Fixes BUG:454880