Overrides correction range units issues

[ps2]

Describe the bug
Overrides store correction ranges without an associated unit. If the user switches their preferred blood glucose unit, the unit will be displayed wrongly. Also, in dev there is this line: https://github.com/LoopKit/Loop/blob/dev/LoopUI/Extensions/ChartPoint.swift#L63, which assumes the unit is mg/dL, which is wrong for users with mmol/L.

The unit of the defined correction range should be stored in the override settings, or enforce a fixed storage unit, like mg/dL.

[Kdisimone]

closed with fix