This is only used in the current PR to avoid ugly
`strprintf(Untranslated("%s:\n%s"), str, MakeUnorderedList(details)`
boilerplate in init code. But in the future the function could be extended and
more widely used to include more details in GUI error messages or display them
in a more readable way, see code comment.
This makes a number of changes:
- Get rid of the verification_progress argument in the node interface
NotifyHeaderTip (it was always 0.0).
- Instead of passing a CBlockIndex* in the UI interface's NotifyHeaderTip,
send separate height, timestamp fields. This is becuase in headers presync,
no actual CBlockIndex object is available.
- Add a bool presync argument to both of the above, to identify signals
pertaining to the first headers sync phase.
