[Package] Initial implementation of Package API

This patch adds the basic interface needed for starting the development
of Package API. In the following patch we will be adding a platform
dependent implementation.

API specification can be found here:
https://developer.tizen.org/dev-guide/2.2.0/org.tizen.web.device.apireference/tizen/package.html

BUG=XWALK-443
[Package] Implement install() and uninstall() methods of Package API

Add support to install()/uninstall() interfaces of Package API.
capi-appfw-package-manager provides the native implementation
that is needed to install/uninstall a package with the specified
package pathi/id.

BUG=XWALK-443
[Package] Implement set/unset PackageInfoEventListener interfaces.

Add support to set/unset PackageInfoEventListener of Package API to
receive or stop notifications for any changes made to the list of
installed packages.

BUG=XWALK-443
[Package] Implement getPackageInfo() and getPackagesInfo() Interfaces.

This is the implementation of Package API getPackagesInfo() and
getPackagesInfo() interfaces using native pkgmgr-info and pkgmgr
APIs.

BUG=XWALK-443
[Package] Add an example for Package API.

This commit includes a example that demonstrates the
usage of Package API.