[Tizen] Add installer update signal and refactored package installer related code

To support "update" signal, a new "--update" argument is added to
xwalk-pkg-helper. The PkgInstaller is also refactored, original
install/uninstall methods are made internal, the public
install/uninstall/update methods will handle these signals sending.

As the package helper is only used by Tizen, remove Linux build for
it. Also put Tizen package insaller related functions to an
PackageInstaller
class, and these service mode checkers are removed from
ApplicationService.

BUG=XWALK-1600