Fix operator id numbering

Proposed changes

The operator ID is represented as a string when it should not, which causes the IDs of new operators to just be old one plus a one, leading to IDs like "9711111111111". This PR fixes that issue.

Types of changes

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[x] Bugfix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

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[x] I have read the CONTRIBUTING doc
[x] I have signed the CLA
[ ] I have added tests that prove my fix is effective or that my feature works
[ ] I have added necessary documentation (if appropriate)
[ ] Any dependent changes have been merged and published in downstream modules

Further comments

None

Wirecloud / wirecloud