Fix EntryView and PreviewView to automatically update when the database changes

[Aetf]

This addresses the concern in #6943 (comment).

DatabaseWidget::deleteEntries does the following things:

1. select row above after deletion
2. refresh the search
3. update preview view

This PR removes 2 and 3 by connecting them to appropriate signals.

A little explanation of why 1 is kept:

Qt already handles selection and current item updates during row removal: when a row is removed, the current item is updated to one of the remaining items; and the row is simply removed from the set of selected rows. This is already the behavior we want in most cases.
The code in 1 additionally makes the new current item the new selection. This is useful in the UI as the user can keep delete entries but is not so useful otherwise.

Testing strategy

• Tested manually that there is no behavior change in the UI (entry selection, preview view)
• Tested manually with FdoSecrets: implement unlock before search #6943 that removal from the background does not break the UI

Type of change

• ✅ Refactor (significant modification to existing code)

[codecov-commenter]

Codecov Report

Merging #7041 (684d565) into develop (b6716bd) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #7041   +/-   ##
========================================
  Coverage    63.61%   63.62%           
========================================
  Files          330      330           
  Lines        41807    41804    -3     
========================================
  Hits         26595    26595           
+ Misses       15212    15209    -3     

Impacted Files	Coverage Δ
src/gui/DatabaseWidget.cpp	61.62% <100.00%> (-0.01%)	⬇️
src/core/Entry.cpp	83.89% <0.00%> (+0.21%)	⬆️

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