[Download] Use new C++ wrapper in common/extension.h

ExtensionAdapater should be deperacated by common::Extension and
common::Instance.
[power] throw an exception instead of blocking forever

In synchronous calls, throw an exception instead of blocking
forever when the underlying system API returns an error.
Modified example to show usage.

BUG=XWALK-1390
Fix build issue on desktop.

libtzplatform-config dependency is introduced by commit 0c5d1dc2, it
should be under Tizen profile only, otherwise desktop will fail to
configure.
Merge branch 'master' of github.com:zolkis/tizen-extensions-crosswalk