Rename variable to parameter or outputValue where applicable

[SanJSp]

Fixes #222

Changes

This PR changes all occurrences of variable in the code with either parameter if it's an input or outputValue if it's an output. I will also update all ssots (ouputVariable to outputValue fields) in the database when this PR is approved 💁‍♂️

If you want an easy teview, check the commits one by one as I have structured them.

Checklist before merge

Developer's responsibilities

• [x] Assign one or two developers
• [ ] Change code if reviewer(s) has/have requested it
• [x] Pull request build has passed
• [x] tested locally (in at least chrome & firefox if frontend)
• [x] updated the documentation
• [ ] added tests where necessary