Add target webodf.js.zip-target
Rename product targets and add consistent prefix "product-"
Note the products which can be built currently in README-Building.md
Add note to remove build target "zip" when CI no longer uses it
Merge pull request #582 from kossebau/CIZip

Add library product (zip with webodf.js + API dox), normalize product build targets, "zip" build target flagged for removal
Fix property removedProperties of ops.OdtDocument.signalMetadataUpdated

was passed as removedProperties.attributes: !string
instead of    removedProperties: !Array.<!string>

also
* reuse initial spec variable
* only deep clone opspec.setProperties, as removedProperties is cloned by
  opspec.removedProperties.attributes.split(',') already
Init removedPropertiesArray to null, is understood by OdfContainer.setMetadata
Add gui.MetadataController
Use filter/join methods of Array for more elegant code
explain unfilteredTagName parameter

fixup Add gui.MetadataController
fix typing of opspec

fixup Fix property removedProperties of ops.OdtDocument.signalMetadataUpdated
Remove dead code from ops.OpUpdateMetadata
move isNotBanned method and list of restricted props out of setMetadata()

fixup for Add gui.MetadataController
shouldBeEffective -> shouldBeUpdated, shouldBeRemoved