Draft: DetailsView : allow to extract and display files metadata without baloo

It allows to extract metadata where baloo does not index files (external drives) and when baloo indexing is set off to feed the details view.

Allow to build without KFileMetaData.

BUG: 406506 FIXED-IN: 21.04

Requires network/kio-extras!51 (closed)

I have had this code lying around since I started the kio-extras patch.

Changes:

• Renames KBalooRolesProviderSingleton to a more generic KMetaDataRolesProviderSingleton, and KBalooRolesProvider to KMetaDataRolesProvider
• Adds a MetaDataExtractorJob using the new metadata ioslave added in network/kio-extras!51 (closed)
• Make the dolphin able to compile without KFileMetadata, and keep some metadata without Baloo
• Allows KFileItemModelRolesUpdater to fallback to the new job when baloo is unavailable or is not enabled for the file considered.

cc @bruns @ngraham