Add support for processing only first occurence of allow-navigation.

Add support for processing only first occurence of allow-navigation.

[Issue#] https://bugs.tizendev.org/jira/browse/TDIS-6856
[Problem] All allow-navigation elements from web application's
configuration document are parsed but only the first one
should be processed.
[Cause] N/A
[Solution] Process only the first occurrence of the allow-navigation
element.
[SCMRequest] Depends on: https://review.tizendev.org/80915
[Verification]
1. Build repository
2. Run test test/tct/wrt/tct-ext02-wrt-tests/setting-an-more

Change-Id: Ief2a0ce2f6a59b40c08df0fa90ffb04caa9377dc