Asserting a schema attribute must require presence of minimal set of attributes

[grigoryk]

These assertions are legit:

[[:db/add "testProp" :db/ident :testProp]]

and:

[:db/add "testProp" :db/ident :testProp]
[:db/add "testProp :db/valueType :db.type/string]
[:db/add "testProp :add/cardinality :db.cardinality/one]]

However, assertion sets which are missing one of the required attributes, such as:

[:db/add "testProp" :db/ident :testProp]
[:db/add "testProp :db/valueType :db.type/string]]

should be illegal.

Similarly,

[[:db/add "testProp :db/valueType :db.type/string]
[:db/add "testProp :add/cardinality :db.cardinality/one]]

should also be illegal.

[grigoryk]

This is relevant to #796 in spirit, although should require much less changes to implement.