Optimize and use SVG images where possible (#281)

SVG images have been optimized with svgo, this will slightly reduce package size though the main reason for this was to remove unneeded markup.

Image paths have been changed and merged, now the directory tree looks like this:

img
├── app
├── material
│   ├── black
│   └── white
└── preview

The reason to merge the paths is to avoid duplicate files for buttons and configuration.

SVG icons are used by default now, PNG images have not been deleted from the images directory, but they were deleted from the graphics.qrc resource file.

All image paths were updated accordingly, except in the tray icon, I could not make it work using the SVG image.

src/widgets/infowindow.cpp

@@ -27,7 +27,7 @@
 
 InfoWindow::InfoWindow(QWidget *parent) : QWidget(parent) {
     setAttribute(Qt::WA_DeleteOnClose);
-    setWindowIcon(QIcon(":img/flameshot.png"));
+    setWindowIcon(QIcon(":img/app/flameshot.svg"));
     setWindowTitle(tr("About"));
 
     m_layout = new QVBoxLayout(this);