[WIP] Sensiolabs Insights improvements

**TODO:**

- [ ] Make deps installable again
- [x] Move security users to ```app/config/parameters.yml```
- [ ] Remove unused code
- [ ] Configure failing checks the right way

**Status Quo:**

[![SensioLabsInsight](https://insight.sensiolabs.com/projects/1e039ee4-b74e-48f6-a583-289a4431ffa9/big.png)](https://insight.sensiolabs.com/projects/1e039ee4-b74e-48f6-a583-289a4431ffa9)
**PR:**

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #254
| License       | MIT
| Doc PR        | none
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