[Feature]: When a user is not or no longer sending `Last seen` status info, remove that info from chat view

### Precondition - [x] I understood that this template is only for feature requests and not for bug reports ### Cross-checked related issues? - [x] I have cross-checked this overview https://github.com/monal-im/Monal/issues/322 as well as filtered for related labels https://github.com/monal-im/Monal/labels ### Describe your feature Currently Even when a user is no longer sending `Last seen` status info, the info `Last seen: n days ago` is still shown in chat view. Expected That is misleading as that info then no longer is accurate. Once detected that the user is no longer sending that information, that info should be hidden. Tested with Conversations (Accounts > Settings > Privacy > Show last seen). An attempt to resolve this was https://github.com/monal-im/Monal/commit/a8531a60ddf59c904e854d0b9810045238bfe408 In latest alpha, the info is still shown. Unsure if that is due to other issues in current alpha which makes it hang fairly quickly after launch. Polite ping @lissine0