Customize buttons on MessageBox and confirm before recycling (#2376)

* Add confirmation prompt before moving groups to the recycling bin

Spawn a yes/no QMessage box when "Delete Group" is selected on a group
that is not already in the recycle bin (note: the prompt for deletion
from the recycle bin was already implemented).  This follows the same
pattern and language as entry deletion.

Fixes #2125

* Make prompts for destructive operations use action words on buttons

Replace yes/no, yes/cancel (and other such buttons on prompts that cause
data to be destroyed) use language that indicates the action that it is
going to take. This makes destructive/unsafe and/or irreversible operations
more clear to the user.

Address feedback on PR #2376

* Refactor MessageBox class to allow for custom buttons

Replaces arguments and return values of type QMessageBox::StandardButton(s)
with MessageBox::Button(s), which reimplements the entire set of
QMessageBox::StandardButton and allows for custom KeePassXC buttons,
such as "Skip". Modifies all calls to MessageBox functions to use
MessageBox::Button(s).

Addresses feedback on #2376

* Remove MessageBox::addButton in favor of map lookup

Replaced the switch statement mechanism in MessageBox::addButton with
a map lookup to address CodeFactor Complex Method issue. This has a
side-effect of a small performance/cleanliness increase, as an
extra QPushButton is no longer created/destroyed (to obtain it's label
text) everytime a MessageBox button based on QMessageBox::StandardButton
is created; now the text is obtained once, at application start up.

src/core/Bootstrap.cpp

@@ -18,10 +18,12 @@
 #include "Bootstrap.h"
 #include "core/Config.h"
 #include "core/Translator.h"
+#include "gui/MessageBox.h"
 
 #ifdef Q_OS_WIN
 #include <aclapi.h> // for createWindowsDACL()
 #include <windows.h> // for Sleep(), SetDllDirectoryA(), SetSearchPathMode(), ...
+#undef MessageBox
 #endif
 
 namespace Bootstrap
@@ -56,6 +58,7 @@ namespace Bootstrap
         setupSearchPaths();
         applyEarlyQNetworkAccessManagerWorkaround();
         Translator::installTranslators();
+        MessageBox::initializeButtonDefs();
 
 #ifdef Q_OS_MACOS
         // Don't show menu icons on OSX