issue y axis bug

Overview

• I limited the max-min difference to 400 because apexcharts doesn't show the plot correctly, when the difference is greater than 400
• I beautified the error state and helperText state
  before: editing one value invalidly and editing the other one, resetted the first value to the last valid value
  now: you can now edit both input values invalidly and it doesn't reset the values (of course it only dispatches if both values are valid)
  also: when input field is empty, it declares it as an error (looks great imo)
  also: I outsourced the error state and helperText state to own functions and replaced inline-if-else with normal if-else (better to read)
• I added JSDoc to the new functions