Fix date parsing for Temp Basals using ISO8601DateFormatter

[bjorkert]

Updated date parsing for basals using a new helper function supporting both Trio and Loop date formats.

[marionbarker]

1. Code review

   • looks good
   • reviewed again after second commit

2. Test

   • tested with a site that would not display basals; with this fix, the basals are displayed properly
   • first commit failed with PR for a Loop URL; after adding second commit succeeds with Loop URL
   • success for Trio URL for 0.2.2 and 0.3.0

[marionbarker]

Test again after additional update that cleans up code even more. This was triggered by noticing a print statement from LoopFollow/Controllers/Nightscout/Treatments/Carbs.swift. @bjorkert then moved "the code from the new function to the global one (NightscoutUtils.parseDate)". This is a better implementation that improves date parsing for carbs as well as basal. (Other treatments already use this function).

1. Code review (over all commits): approved
2. Tests successful for
   • URL that had initial problem displaying basals
   • Loop URL
   • Trio 0.2.2 and 0.3.0 URLs