Made header blobs larger and odd number of pixels in size so that minus and plus signs can be centred.
Made header blobs larger and odd number of pixels in size so that minus
and plus signs can be centred.

rhaberkorn/scintilla-mirror,rhaberkorn/scintilla-mirror,rhaberkorn/scintilla-mirror,rhaberkorn/scintilla-mirror,rhaberkorn/scintilla-mirror,rhaberkorn/scintilla-mirror,rhaberkorn/scintilla-mirror,rhaberkorn/scintilla-mirror