Add horizontal line with current price

[thmeta]

Is your feature request related to a problem? Please describe.
No

Describe the solution you'd like
A horizontal line showing the current price (ticker)

Describe alternatives you've considered
No

Additional context
The ticker data is already there, ie. Current Rate under Open Trades, so perhaps it "just" a matter of adding it to the chart. Could be helpful especially for higher timeframes like 1h, 4h...

[xmatthias]

I'm not entirely sure that having such a line is "that" great an idea - at least not without the option to disable the line.

Charts can become pretty messy pretty quickly - and relying on "current_rate" will provide a delayed reponse - as current_rate is (potentially) cached in the backend (for API use, anyway).

It'll refresh every few seconds in the frontend - but i don't think it'll update reliably in all scenarios - as it's not actually relevant for bot operations, and only provided via API as "convenience" from the last used rate.