Right Y-axis for HR

[morteako]

• Adds right y axis to be able to see hr-changes better, with a smaller domain. +-20 seems To be decent in not being too large and also not too small, so that very small jumps actually seems small
• Adds coloring and labels to the y-axises
• Adds -2:00, -4:00 and -6:00 ticks to x axis
• Adds x-axis (or just a line) below the PowerBar. Added to have the charts aligned, but actually looks more neat (to me)
• Chore🤠: Renames PowerChart to DataChart

HR

Power

Starting page changes

Current

PR: Starting page

I guess the x-axis ticks could be confusing. But so is also the 1-2-3-4 y axis in the power bar. I don't think the changes to the starting page here are a blocker, but if it is. I think maybe the solution is to maybe hide both charts when the are noe data to display. Should pretty easy. WDUT, @sivertschou ?

[sivertschou]

Not sure what I think about the X axis, but that can be changed later