Improve reserved keyword error ; add tests

[mariusconjeaud]

Make sure to return ValueError with explanation for reserved keywords :

• Nodes :
  • deleted
  • id
  • element_id
• Rels :
  • source
  • target

Includes test coverage

[mariusconjeaud]

Issue #590

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.07% :tada:

Comparison is base (90b7a5d) 86.17% compared to head (2a3636b) 86.25%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## rc/5.1.2 #746 +/- ## ============================================ + Coverage 86.17% 86.25% +0.07% ============================================ Files 19 19 Lines 2395 2401 +6 ============================================ + Hits 2064 2071 +7 + Misses 331 330 -1 ``` | [Files Changed](https://app.codecov.io/gh/neo4j-contrib/neomodel/pull/746?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=neo4j-contrib) | Coverage Δ | | |---|---|---| | [neomodel/core.py](https://app.codecov.io/gh/neo4j-contrib/neomodel/pull/746?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=neo4j-contrib#diff-bmVvbW9kZWwvY29yZS5weQ==) | `95.26% <100.00%> (+0.37%)` | :arrow_up: | | [neomodel/relationship.py](https://app.codecov.io/gh/neo4j-contrib/neomodel/pull/746?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=neo4j-contrib#diff-bmVvbW9kZWwvcmVsYXRpb25zaGlwLnB5) | `97.29% <100.00%> (+0.07%)` | :arrow_up: |

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