feat(id): produce UUID with `generateId`

[TonyMasse]

This is the replace the much simpler but prone to problem simple (and small) random Integer generation. Additionally, I kept the function definition to DiagramModel.js only, and imported it from the other places where it's needed.

Close #14

What kind of change does this PR introduce? (check at least one)

• [ ] Bugfix
• [x] Feature
• [ ] Code style update
• [ ] Refactor
• [ ] Build-related changes
• [ ] Other, please describe:

Does this PR introduce a breaking change? (check one)

• [ ] Yes
• [x] No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• [ ] It's submitted to the develop branch (or to a previous version branch), not the master branch
• [x] When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• [x] All tests are passing
• [ ] New/updated tests are included

If adding a new feature, the PR's description includes:

• [x] A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

[TonyMasse]

Managed to good this again and bring in tons of Commits from other branch... Closing this PR and going to open a new one.