[master < T0115-GA] Fix Datetime serialisation

[katarinasupe]

Description

I added all Datetime types check when serializing class properties in the escape_value procedure. Also, the repr was called instead of escape_value procedure. I also added a small change in README regarding Conda environment.

Pull request type

Please delete options that are not relevant.

• [x] Bugfix

Related issues

Closes https://github.com/memgraph/gqlalchemy/issues/183

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

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