Adding flexible day calendar

[araujoarthur0]

Related issue

Closes #369

Context / Background

This PR introduces a Day Calendar with a flexible number of entries :)

What change is being introduced by this PR?

• New button on Flexible Month Calendar to switch to Day Calendar
  

• Changes on preferences to allow flexible + day

• New FlexibleDayCalendar class built in the same idea of the FixedDayCalendar, but with the structure of FlexibleMonthCalendar

• Entry pairs are added on new rows in the table, with intervals between them

• To add an entry there is a button near the day total box

• To remove the last entry there is a dialog to confirm removal (button appears when there are more than 2 pairs of entries)

• Input errors color the entry row with the error
  

How will this be tested?

New tests were added following the idea of the other Calendar tests.

[codecov]

Codecov Report

Merging #379 into main will increase coverage by 1.51%.
The diff coverage is 63.71%.

@@            Coverage Diff             @@
##             main     #379      +/-   ##
==========================================
+ Coverage   55.21%   56.72%   +1.51%     
==========================================
  Files          24       25       +1     
  Lines        2063     2373     +310     
  Branches      348      401      +53     
==========================================
+ Hits         1139     1346     +207     
- Misses        818      908      +90     
- Partials      106      119      +13     

Impacted Files	Coverage Δ
src/preferences.js	0.00% <ø> (ø)
js/classes/FlexibleMonthCalendar.js	54.40% <37.50%> (-0.10%)	⬇️
js/classes/FlexibleDayCalendar.js	65.78% <65.78%> (ø)
js/classes/CalendarFactory.js	66.66% <70.00%> (ø)
js/classes/Calendar.js	68.64% <100.00%> (ø)
js/date-db-formatter.js	100.00% <100.00%> (ø)
js/user-preferences.js	92.45% <100.00%> (-0.14%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 82d51a0...0a09a37. Read the comment docs.

[thamara]

Apart from my comment regarding the alignment of the content in the day view and the reuse of the API for formating the key, I think the PR is in pretty good shape.
I see a lot of code that is duplicated from the fixed calendar, but I think we most likely we'll replace completely the fixed one, so it should not be a problem.
Once this PR is done, I think we need to discuss a bit on the future of TTL w.r.t. the fixed vs flexible DBs.

[araujoarthur0]

Yeah, I decided to copy styles and functions instead of reusing them from the other day calendar because we're still discussing that.
If we don't drop, I'm really going to advocate for a .scss styles organization, because we're over 1000 lines on our monolithic styles file 😋

[araujoarthur0]

Using generateKey, updated documentations to fit my other PR and alignment fix.