GWT: 0.6.1, verify .properties files syntax and values types and syntax conformity before using configuration files

verify the following files at startup:

• textometries.properties
• twmweb.conf

1. syntax conformity
2. values types and syntax conformity
   • example : path, integer…

(from redmine: issue id 2516, created on 2019/03/13 by Serge Heiden)