Convert from using string to enum values for severity in ErrorItem.
Storing and handling severity as string was the easy way earlier
but it is not convenient or efficient way to handle severities.
This commit is the first step in converting severity handling to
use the enum values instead of strings.
Debug errors were not shown anywhere in the GUI, they were just
ignored. This commit adds new signal for those debug errors and
directs them to checking log.
Solves ticket #1898 (GUI: Handle internal errors from lib)
This commit modifies and registers ErrorItem as proper metatype so it
can be used with Qt signals. Then sending Error-signals is refactored
so that ErrorItem instances are sent instead of several different
arguments that already contained couple of lists.
Kimmo Varis
Reijo Tomperi
Daniel Marjamäki