Add option for flat bar

[AlexPerathoner]

Discussed in https://github.com/AlexPerathoner/SlimHUD/discussions/31

^{Originally posted by **coffinmilk** September 11, 2022} Although most might prefer the inside of the bar to be rounded, for iOS consistency, can the bar be made flat?

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Add option for flat bar

Steps:

• [x] In Displayer.swift:setThickness( ... ) add option to change barView.bar.progressLayer.cornerRadius = thickness/2 to barView.bar.progressLayer.cornerRadius = 0
• [x] Add option in settings
• [x] Add to UserDefaults

Result: