imageView: Use large icons for zoom buttons

The small +/- buttons are reserved for spin rows. Otherwise the large
ones should be used.

data/resources/icons/scalable/actions/minus-large-symbolic.svg

@@ -1,2 +1,2 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<svg xmlns="http://www.w3.org/2000/svg" height="16px" viewBox="0 0 16 16" width="16px"><path d="m 3 7 h 10 v 2 h -10 z m 0 0" fill="#222222"/></svg>
+<svg xmlns="http://www.w3.org/2000/svg" height="16px" viewBox="0 0 16 16" width="16px"><path d="m 1 7 h 14 v 2 h -14 z m 0 0" fill="#222222"/></svg>

data/resources/icons/scalable/actions/plus-large-symbolic.svg

@@ -0,0 +1,2 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" height="16px" viewBox="0 0 16 16" width="16px"><path d="m 7 1 v 6 h -6 v 2 h 6 v 6 h 2 v -6 h 6 v -2 h -6 v -6 z m 0 0" fill="#222222"/></svg>

data/resources/icons/scalable/actions/plus-symbolic.svg

@@ -1,2 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<svg xmlns="http://www.w3.org/2000/svg" height="16px" viewBox="0 0 16 16" width="16px"><path d="m 7 3 v 4 h -4 v 2 h 4 v 4 h 2 v -4 h 4 v -2 h -4 v -4 z m 0 0" fill="#222222"/></svg>