Upgrade to Grakn 1.8

[jmsfltchr]

What is the goal of this PR?

Upgrade KGLIB to work with Grakn 1.8.0, and to use the associated updates to the graknlabs build systems

What are the changes implemented in this PR?

• Update build elements to conform to the latest dependency style in graknlabs
• Incorporate the syntax changes present in Grakn 1.8, datatype -> value, date -> datetime