[GSoC] Refactor ArchiveNode and ArchiveDirNode classes

Refactor ArchiveNode and ArchiveDirNode classes to Archive::Entry class
and move its declaration to kerfuffle/archiveentry.h file.

Make Archive::Entry store meta data in Q_PROPERTY members.

Move EntryMetaDataType to part/archivemodel.cpp.

Delete duplicated directory entries while reading from 7z archives.

See:
https://phabricator.kde.org/T2704