Move GetConfigPath to GetAppPath (applications directory)

BUG: XWALK-2672

Change-Id: Iee497d8f5744b1d8c4533fe7f6009040b0bcf826
Signed-off-by: Sabera Djelti (sdi2) <sabera.djelti@open.eurogiciel.org>
Why isn't this one `const`?