Dynamic function to test for core contributor flag

This removes the isCore flag and allows us to dynamically calculate the
core flag for contributors.

For now this is just us (the first 6 contirbutors)

Also we do not need the default contributor anymore because the deploy
user has the role to manage contributors and can create the first real
contributors.

lib/contracts/contributor.js

@@ -67,7 +67,6 @@ class Contributor extends Base {
           ipfsHashAttr.hashDigest,
           ipfsHashAttr.hashFunction,
           ipfsHashAttr.hashSize,
-          contributorAttr.isCore,
         ];
 
         return this.functions.addContributor(...contributor, callOptions);