Move EnginioReply properties to public section

Technically Q_PROPERTY macro is empty, but it was looking awkward.
First step of EnginioReply refactoring.

Rename errorCode to networkError, new enum ErrorTypes was added,
error notification signals were combined together.
Add more sophisticated error checking in autotests
Do not define global static objects in a header file.
Merge pull request #99 from nierob/errorHandling

Error handling