Needed infrastructure changes were done in ArchiveFormat, CliProperties and
other classes. A combobox was added to CreateDialog which enables setting the
encryption method.
Currently, only the Zip format when using cli7z supports multiple encryption
methods. For other formats that support only one encryption method, the method
is shown in the combobox.
This diff also enables detection of encryption method when opening archives
which is then shown in PropertiesDialog. To this end a new signal was added to
ReadOnlyArchiveInterface (encryptionMethodFound). The similar
compressionMethodFound signal was modified to only take one string instead of
QStringList.
