GWT: 0.6.1, Synchronize Simple_Viewer_beta usage between XTZ import module and TXM portal

Currently, the viewer (zoom, pan, etc.) does not work on corpora created with XTZ module due to difference in file names. See email by Lars Döhling :

1. TXMWEB.jsp refers to Simple_Viewer_beta_1.1.js instead of Simple_Viewer_beta_1.1-min.js
--> fix: added "-min" in @src

2. The viewer images are located in images/toolbar as specified by viewer.toolbarImages 
inside toolbar-ext.js. However, all facs html files redefine viewer.toolbarImages to 
images/icons where they are located in the TXM file (but not at the portal).
--> fix: copied toolbar/*.png to icons, as symlinks do not work here

I think a better solution would be to keep the default path images/toolbar, i.e. fix the 
TXM file by removing the viewer.toolbarImages redefinition and rename images/icons 
to images/toolbar. 

(from redmine: issue id 2269, created on 2017/10/18 by Alexey Lavrentev)