Allow setting group icons to children groups/entries

[ghost]

Set an icon for a group and automatically use it for subgroups and
subentries.

Type of change

• ✅ New feature (non-breaking change which adds functionality)

Description and Context

Applying icons recursively can be helpful if the database owner follows a policy
in which entries always have the same icon as their parent group (which also is
the standard setting for new entries).
After reorganization of the database, the icons keep their old icon which was
the icon of their old parent.
To avoid setting the icon of each entry individually, a new checkbox is
introduced in the "Icon" category of the EditGroupWidget.
Since the EditIconWidget is also used by the EditEntryWidget, the checkbox
also appears there but checking the box has no effect in this case.

The ApplyGroupIconTo(Entry*) is adjusted to be more generally applicable. Until now, the method was intended to be only run on entry creation (config checks).

Fixes #3228
Fixes #1314
Fixes #2361

Screenshots

After reorganization of the entries, the icons of the entries are mingled
wildly.

To match the icons of the entries to their new parent group, open the edit mode
of the parent and select the icon.

To apply the icon recursively, check the box.
A message box requests confirmation to ensure that the option is checked
intentionally, to avoid accidental overwriting of icons.

Testing strategy

A new unit test is introduced in TestGroup which tests the new option with
a database which contains two nested subgroups in the root group.
Setting the icon by number as well as UUID is tested.

Checklist:

• ✅ I have read the CONTRIBUTING document. [REQUIRED]
• ✅ My code follows the code style of this project. [REQUIRED]
• ✅ All new and existing tests passed. [REQUIRED]
• ✅ I have compiled and verified my code with -DWITH_ASAN=ON. [REQUIRED]
• ✅ My change requires a change to the documentation, and I have updated it accordingly.
• ✅ I have added tests to cover my changes. [x]

Possible alternative

Another possible method would be to introduce an option in the context menu of
selected entries.

Annotations

ASAN reports a memory leak if a custom icon is added or deleted (libglib).
This leak already existed in previous commits (and is not addressed by the
proposed changes).

Two new strings are introduced (checkbox and message box) and need to be
translated.

[ghost]

Thanks for your annotations. I tried to correct all of them.

I tried to prevent to blue folder icon being set to an entry on entry creation as requested. But if the user chooses the folder icon for an entry and decides to "Apply the icon to child entries" (or all children too), the blue folder icon will be set (as the user has requested it actively). I hope that this is ok.

[droidmonkey]

Yes if the user explicitly selects the blue folder and asks to apply to everything then that should be allowed. In fact that fixes and issue we have!

Love the combo button!

[affinityv]

I don't know if this is related, but I had some weird icon changes to the blue folder for ordinary entries; I've manually changed the icons for those random entries. I've used various versions over time, first noticed this issue with 2.4.3 though, but it may have been there already (if it was I don't know when it occurred exactly).