New unary option readOnly to declare an entity as read-only

[murdos]

Fixes #318

I used the keywork readOnly, but only at end I realized that it could have been readonly (both are used in #318).
Please let me know what you prefer, and I'll update the PR.

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[MathieuAA]

Thanks @murdos I'll test this out ASAP!

[MathieuAA]

Except the missing test, everything's perfect

[MathieuAA]

missing a test here:

• add in the Employee.json file (used in this converter's test file) this entry "readOnly": true.
• in the test, l.156, add this:

          expect(
            jdlObject
              .getOptions()
              .filter(option => option.name === UnaryOptions.READ_ONLY && option.entityNames.has('Employee')).length
          ).to.equal(1);

[murdos]

Thanks. I'm going to add the missing test.
So do we keep readOnly or readonly?

[MathieuAA]

readOnly is good, let's keep it this way

[murdos]

Ok. Missing test has been added

[MathieuAA]

Thanks :)

[MathieuAA]

Alright, let's merge it. Thanks @murdos!