Pipeline rules: changing name of rule breaks pipeline

If you change the name of a rule, then any pipeline it is used in now shows "_Rule has been renamed or removed. This rule will be skipped._". This then requires the user to remove and re-add the rule to the pipeline.
## Expected Behavior

Upon changing a rule's name, the pipeline should continue to reference the rule, and display it under its new name in the same position in the same stage.
## Current Behavior

Upon changing a rule's name the pipelines that use the rule can no longer find the rule and therefore show an alert in the Pipeline's summary page.
## Possible Solution

Link rules into pipelines using an internal unique id, not the rule name (if, as it appears, that is what is currently done).
## Steps to Reproduce (for bugs)
1. Create a rule
2. Create a pipeline
3. Add the rule to the pipeline's stage
4. Edit the rule and change its name
5. Review the pipeline summary (System > Pipelines > Manage Pipelines > Edit pipeline)
6. Note the warning next to the rule's old name
## Context

This is just a pain - as a graylog setup evolves and is refactored to add standardisation of rule names to help with cross-team management of graylog, renaming rules is inevitable.
## Your Environment
- Graylog Version: 2.0.3 (f07c170)