fix(NcDateTimePicker): improve some usability issues

[GVodyanov]

Fixes a few small issues:

• Selected offset/disabled days now have white text color
• Added icon to submit button
• Fixed scrolling through the months. Previously horizontal scroll made it go to the past, and vertical to the future, which is really weird. Now scrolling to left/right goes past/present.

🖼️ Screenshots

🏚️ Before	🏡 After

🚧 Tasks

• ...

🏁 Checklist

• ⛑️ Tests are included or are not applicable
• 📘 Component documentation has been extended, updated or is not applicable
• 2️⃣ Backport to stable8 for maintained Vue 2 version or not applicable

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.55%. Comparing base (034beb5) to head (58cbf03).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8479   +/-   ##
=======================================
  Coverage   54.55%   54.55%           
=======================================
  Files         106      106           
  Lines        3439     3439           
  Branches     1002     1003    +1     
=======================================
  Hits         1876     1876           
  Misses       1322     1322           
  Partials      241      241           

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[SebastianKrupinski]

Looks good