Revise: switch to using icons from theme for show/hide password

And provide some `.png` icons if they are not in the current desktop theme
(on Linux/FreeBSD) or the OS does not provide such a system for them...

These icons were created by myself and I will licensing them under GPL 2.0
(or later terms).

Signed-off-by: Stephen Lyons <slysven@virginmedia.com>

src/dlgConnectionProfiles.cpp

@@ -2411,11 +2411,11 @@ void dlgConnectionProfiles::slot_togglePasswordVisibility(const bool showPasswor
         // In practice I could not get the icon to change based upon supplying
         // different QPixmaps for the QIcon for different states - so lets do it
         // directly:
-        mpAction_revealPassword->setIcon(QPixmap(QStringLiteral(":/icons/layer-visible-on.png")));
+        mpAction_revealPassword->setIcon(QIcon::fromTheme(QStringLiteral("password-show-on"), QIcon(QStringLiteral(":/icons/password-show-on.png"))));
         mpAction_revealPassword->setToolTip(tr("<p>Click to hide the password; it will also hide if another profile is selected.</p>"));
     } else {
         character_password_entry->setEchoMode(QLineEdit::Password);
-        mpAction_revealPassword->setIcon(QPixmap(QStringLiteral(":/icons/layer-visible-off-redlined.png")));
+        mpAction_revealPassword->setIcon(QIcon::fromTheme(QStringLiteral("password-show-off"), QIcon(QStringLiteral(":/icons/password-show-off.png"))));
         mpAction_revealPassword->setToolTip(tr("<p>Click to reveal the password for this profile.</p>"));
     }
 }

src/mudlet.qrc

@@ -107,8 +107,6 @@
         <file>icons/imperian_120_30.png</file>
         <file>icons/import.png</file>
         <file>icons/internet-telephony.png</file>
-        <file>icons/layer-visible-off-redlined.png</file>
-        <file>icons/layer-visible-on.png</file>
         <file>icons/luminari_icon.png</file>
         <file>icons/lusternia_120_30.png</file>
         <file>icons/media-optical.png</file>
@@ -136,6 +134,8 @@
         <file>icons/offsettimer-on.png</file>
         <file>icons/package-manager.png</file>
         <file>icons/package-exporter.png</file>
+        <file>icons/password-show-off.png</file>
+        <file>icons/password-show-on.png</file>
         <file>icons/Patreon_Mark_Primary.png</file>
         <file>icons/place_of_interest.png</file>
         <file>icons/preferences-desktop-keyboard.png</file>