permit install into windows program files

when installing terasology into program files, that dir is not writeable.
starting up, terasology tries to create a folder in .local, which then
fails.

therefor, permit two things with this change. first, permit calling
the windows bat script from a different directory. it then needs to
find the library relative to the start script location, not to the
location where the script is called from.

second, before starting java, change to home directory. ideally,
terasology itself should find a proper path by default. but
program files as run directory is in any case wrong, so change.

facades/PC/src/main/startScripts/windowsStartScript.bat.gsp

@@ -62,8 +62,9 @@ goto fail
 
 <% if ( mainClassName.startsWith('--module ') ) { %>set MODULE_PATH=$modulePath<% } %>
 
-@rem Execute ${applicationName}
-"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %${optsEnvironmentVar}% <% if ( appNameSystemProperty ) { %>"-D${appNameSystemProperty}=%APP_BASE_NAME%"<% } %> <% if ( mainClassName.startsWith('--module ') ) { %>--module-path "%MODULE_PATH%" <% } %>-jar lib\\Terasology.jar %*
+@rem Execute ${applicationName} in home directory
+cd /d %homedrive%%homepath%
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %${optsEnvironmentVar}% <% if ( appNameSystemProperty ) { %>"-D${appNameSystemProperty}=%APP_BASE_NAME%"<% } %> <% if ( mainClassName.startsWith('--module ') ) { %>--module-path "%MODULE_PATH%" <% } %>-jar "%APP_HOME%\\lib\\Terasology.jar" %*
 
 :end
 @rem End local scope for the variables with windows NT shell