Core API: add an AssocDef in the middle of the sequence

[jri]

Currently the API allows only to add an Association Definition at the end of the sequence.

[Jörg Richter <jri@…>]

In 59ee5d08e06fbfc9f394393d4c1b92a134f0d936/deepamehta:

Core API: insert AssocDef? in-mid sequence (#770).

1 new method in Type interface:

void addAssocDefBefore(AssociationDefinitionModel assocDef, String beforeChildTypeUri)

Like addAssocDef() but adds an assoc def before another assoc def, that is inserting it in the midde of the sequence.

1 new general utility class in de.deepamehta.core.util

SequencedHashMap<K,V>

A LinkedHashMap that provides a putBefore(K key, V value, K beforeKey) method to insert an entry before another entry.

See #770.

[Jörg Richter <jri@…>]

In 7e6a2d7910a78b7f49ea96b5899c17df1fbf8ad9/deepamehta:

Core: refactor assoc def sequence storage (#770).

See #770.