Fix target/source keymapping

[thomcom]

Previously, the index value referred to by a graphology graph edges list in the source and target values was being used to lookup nodes according to their position in the nodes array. This is incorrect.

This bugfix creates the key=>index mapping so that source and target refer to nodes by their key entry, not their list position.

This bugfix also moves the default index.js execution of @rapidsai/demo-api-server to port 3010, compatible with the sigma.js demo.

Finally this bugfix adds .setNullMask after the getJSONObject calls, as spurious entries in the nullmask are occurring there since the original merge #392

[AjayThorve]

@thomcom not sure if it's because of this PR or the previous one, but I cannot run the demo locally:

Error: Cannot find module '../util/schema.js'
Require stack:
- /opt/rapids/node/modules/demo/api-server/routes/root.js

seems like ./util/schema.js is missing?

[thomcom]

@thomcom not sure if it's because of this PR or the previous one, but I cannot run the demo locally:

Error: Cannot find module '../util/schema.js'
Require stack:
- /opt/rapids/node/modules/demo/api-server/routes/root.js

seems like ./util/schema.js is missing?

Oh yeah, that's extremely important, thanks for the catch.

[thomcom]

@thomcom not sure if it's because of this PR or the previous one, but I cannot run the demo locally:

Error: Cannot find module '../util/schema.js'
Require stack:
- /opt/rapids/node/modules/demo/api-server/routes/root.js

seems like ./util/schema.js is missing?

Oh yeah, that's extremely important, thanks for the catch.

Also @trxcllnt this makes me pretty stressed out because I see that we're not running any tests as part of CI/PR approval?