Tracking weight for every set of an exercise

[JohannSiemens]

Value proposition:

As a user i want to track my weights for every set of an exercise i do to be able to see if i am getting stronger.

Acceptance criteria:

• [x] There should be a numeric input field for weight for every set within an exercise
• [x] The weight should be displayed for every set, next to the repetitions field
• [x] The weight should be stored within the database

Tasks:

• [x] Create branch
• [x] Change the data model to accept weight as a number value
• [x] Change the client to have an input field for weight
• [x] Change the client to display the weight from the database
• [x] Change the API to also write and read the weight for every set

[JohannSiemens]

QA feedback will be implemented in another PR, successfully merged