Rename the whole project shorter

There is no point in claiming speed, it turns out to be a strange focus
to have, considering the amount of available innovations to make.

The new name does not appear to be taken by anything important.

fiv.desktop

@@ -0,0 +1,10 @@
+[Desktop Entry]
+Type=Application
+Name=fiv
+GenericName=Image Viewer
+Icon=fiv
+Exec=fiv -- %u
+Terminal=false
+StartupNotify=true
+Categories=Graphics;2DGraphics;Viewer;
+MimeType=image/png;image/bmp;image/gif;image/jpeg;image/webp;