Allow future carbs

[bjorkert]

Solves: #242

This PR introduces significant improvements in the way our codebase handles date and time operations. I have consolidated multiple date-time-related functions into a single, more versatile function named getDateTimeString. This refactoring includes:

• Replacing getCurrentDateTimeString, nowMinusNHoursTimeInterval, and nowMinus60DaysTimeInterval with a unified method.
• Enhancing code maintainability and readability by reducing redundancy.
• Allowing for greater flexibility in generating date-time strings, which can now easily handle both past and future dates.

Specifically, this new approach is leveraged to facilitate downloading of future carbohydrate entries (and other treatments) up to 6 hours ahead.

[marionbarker]

Question - should the carbs in future be plotted on the prediction plot?

Test Details

Display Carbs today at top of the information stack

With LoopFollow main branch,

• Carbs today = 15 even though Loop uploaded 15 g at 07:37 (in the past) and 30 g at 12:42 (4 hours in the future)
• Configure graph to show 4.5 hours of prediction
• Carbs not plotted on prediction plot

Rebuild with changes from this PR:

• Carbs today = 45
• Carbs not plotted on prediction plot

[marionbarker]

Future carbs are now plotted when the graph settings are increased.

• Tested hours of prediction = 5
• Entered future carbs 4 hours in future
  • they show up both in Carbs today and in the prediction plot
  • may need to drag the plot to the left to see the full prediction range

Tested the use of password for entering URL.

• The URL and password are added to line from the password store
• This works but is inconsistent with password needed for Loop, which is URL plus API_SECRET.
• It would be convenient if URL would accept an embedded token (as supplied by clicking on access token in Nightscout).

But these modifications should be handled in a separate PR, not bundled with future-carbs.