lift the 6 concurrent daemon access limit

[MichaelMure]

We use QNetworkAccessManager to access the daemon via the http API.

QNetworkAccessManager has a hardcoded limit at 6 concurrent access (https://github.com/qtproject/qtbase/blob/dev/src/network/access/qhttpnetworkconnection.cpp#L63)

It seems to slow down things (more test needed here to be sure).

A solution might be to use multiple instance of QNetworkAccessManager and load balance between them.

[MichaelMure]

We now parse ipfs's stderr to track block locality, so we don't request ipfs refs local anymore.