Fix documentation warnings.
Use consistent naming convention.

Rename all local EnginioReply pointers to "ereply".
Fix crashes in EnginioModel when EnginioClient is not set.
Mark some methods with Q_REQUIRED_RESULT

All methods without side effects can be marked with Q_REQUIRED_RESULT
so compiler warn if result is not used.
Merge pull request #183 from nierob/master

Small improvements