Logging pipeline error/exceptions

[NPavie]

A user reported a "lame not found" issue on a conversion to daisy book.
In this case, the pipeline did not provide details on the exception to the users, while this exception can occured on several occasions, including on a lame encoding issue.
On encoding issue, the pipeline would print errors informations on the stderr output and encapsulate the encoding exception under a "lame not found" exception, the top level exception message being displayed to user.

For better debug/assistance to users in case of pipeline errors, we need to log those errors (and exceptions stacktrace if possible) on a file, that we could retrieve or ask the user to send it to us.

[NPavie]

Messages from pipeline 1 stdout and stderr are being logged back onto the message queue displayed to the user

see commit a3e045c