Add support for a webpage to create +edit rumbas questions / exams

[jhoobergs]

• Add a proc_macro to create Yew components for each datatype

• Add a command to start a webserver that uses these components to visualise the question / exam data

  • The documentation strings would automatically be show as explanation

• Keep track in Value from where the used value comes (and which other values could have been inserted)

• Last step: allow these values to be changed through the ui.