Problem displaying content from the merger site that was not yet downloaded - ZeroMe "User not found or muted"

### Environment

* ZeroNet version: 4210
* Operating system: Windows
* Web browser: FF

#### Issue:

Newbie zeronet user is linked to my ZeroMe profile page (http://127.0.0.1:43110/Me.ZeroNetwork.bit/?Profile/siteaddr/userpubkey/abc@zeroid.bit), but it says to him "User not found or muted".

The cause is possibly that he has not yet downloaded my hub. This is one of the inconveniences of the zeronet and i think it is not only problem of zerome but other zites like Millchan where people can cross link to different hub, but the hub was not yet downloaded thus showing misleading message "Not found" while content is available, just not downloaded.

Why not to make zeronet to work differently so it:
1. detects the site is not yet downloaded
2. A) displays prompt to the user whether he want to download site in order to proceed
B) to prevent downloading large data, download only requested users content from that site ([some downsides & solutions of this approach](https://github.com/HelloZeroNet/ZeroNet/issues/1992#issuecomment-484808086))
3. show progress bar and display the content once the download is complete, so user know the content may appear with a delay.

No source files or tests are named. Start by reproducing the ZeroMe profile link on ZeroNet 4210 on Windows with Firefox while the referenced hub is not downloaded, then trace how the request produces “User not found or muted.” Done means detecting the missing site, obtaining the requested content with visible progress, and displaying it after download without unnecessary large downloads.

Written by the indexing model from the issue text.