[ ] Layout definition without process is supported now
### Checklist
To ensure you provided everything we need to look at your PR:
* [ ] **Brief textual description** of the changes present
* [ ] **Visual demo** attached
* [ ] **Steps to try out** present, i.e. [using the `@bpmn-io/sr` tool](https://github.com/bpmn-io/sr)
* [ ] Related issue linked via `Closes {LINK_TO_ISSUE}` or `Related to {LINK_TO_ISSUE}`
Closes #46
Proposed Changes
- [ ] Layout definition without process is supported now
### Checklist To ensure you provided everything we need to look at your PR: * [ ] **Brief textual description** of the changes present * [ ] **Visual demo** attached * [ ] **Steps to try out** present, i.e. [using the `@bpmn-io/sr` tool](https://github.com/bpmn-io/sr) * [ ] Related issue linked via `Closes {LINK_TO_ISSUE}` or `Related to {LINK_TO_ISSUE}`