Added method to find all Datasets linked to a certain image
Added Multiple-Dataset warning dialog #11883

When the user wants to delete an image which is linked to multiple datasets a warning dialog will be shown, see trac #11883
Added empty method to NullOmeroPojoService to match OmeroDataService interface
Added comment, updated copyright date
Corrected copyright date
Initial working Java MapField
Nearly working c++ map type
Work-around c++ std::map copy semantics

For the moment, getConfig and setConfig are a bit
surprising since the std::map is being passed by
value rather than reference.
Passing Python test
Warning dialog now shows information about the linked Datasets
Removed thumbnails from multiple dataset links warning dialog
Merge remote-tracking branch 'origin/develop' into dsl-map-type

Conflicts:
	etc/omero.properties
OMERO5.1DEV_3: Add MapAnnotation type

This adds an Annotation subclass which has a single
`mapValue` of `<String, String>` type. This may already
point to an issue in the design if we want to have
`<String, Object>` support.
Cleanup test imports
Changed to a more performant database query
fill OMSC stubs for new methods, to appease travis
Make value of maps NON-NULL

Since Ice converts a null string to an empty
string, this change as it stands will store
empty strings in the DB. An RType will be
required to prevent that.
fix javadoc param typo
adjust XML mapping files
introduce String to RString maps into model