Unambiguous usage of data source ID and title

[forman]

Expected behavior

DataSource interface should expose a unique ID and a human-readable title.

However: DataSource.matches_filter(self, query=None)!

Actual behavior

We have DataSource.name which is ambiguous.

Specifications

Cate 0.9.0.dev4

[forman]

Summary of changes:

• renamed property cate.core.ds.DataSource.name to id
• renamed property cate.core.ds.DataStore.name to id
• renamed and changed signature of function cate.core.ds.DataStore.query_data_sources(..., name=None)
  to find_data_sources(..., id=None, query_expr=None)
• changed signature of method cate.core.ds.DataStore.query(name, ...) to query(id=None, query_expr=None, ...)
• renamed and changed signature of method cate.core.ds.DataSource.matches_filter(name) to matches(id=None, query_expr=None)
• added title property to cate.core.ds.DataStore and cate.core.ds.DataSource
• made use of the new id and title properties of both DataStore and DataSource in their
  JSON representations.