[lehni]

Closes #538

Strict insertGraph() with added: 'relate' related ids that don't exist unchecked, since 4.3.0. It now looks them up before anything is written, with the same id-only query that upsertGraph() runs for related models since #372, and throws the same NotFoundError:

model (id=1000) does not exist. If you want to insert it with an id, set added: 'insert' for model1Relation1 in the relations option

• loadCurrentGraph()'s final existence check is now markMissingModels(), which loadRelatedIds() also runs for strict inserts. Non-strict insertGraph() stays unchecked, as in 3.x.
• The hint names added: 'insert' for insertGraph(), which has no relateOrInsert.
• Behaviour change: strict inserts that wrote keys pointing to no row now throw, at the cost of one query per related model class.