Actual soil moisture conversion

[BioBoost]

• Add type of measurement sample
• Implement basic linear interpolation conversion model
• Convert last_value and values using conversion model when applicable. This closes #138, closes #160

[BioBoost]

This should be ok now.

Refactored some of the hooks to middleware functions. Also reworked some of the join functions so they could be re-used in the find() method.

Also changed the conversion function so it could handle all three cases of sensors (single, paginated and joined via tree).

[Phasmatrix]

Everything looks good, will have to change my postman runners to work again with updates. Was not able to test completely due to the fact that my postman runner did not create all devices. Will finish this tomorrow.

[Phasmatrix]

Doublechecked everything and it works as expected.