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.
Ticket #2513 (GUI: Garbage printed to log after missing include warning)
The linenumber was not properly converted to the QString so there
were garbage printed to the log.
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)
Kimmo Varis
Reijo Tomperi