Move pkg_initdb implementation to app-installers

Move pkg_initdb implementation to app-installers

New binary name is: /usr/bin/pkg-initdb

Scripts that creates image should switch to new binary when ready
by changing called binary to given one (then old one may be removed).

/usr/bin/pkg-install-manifest will be removed in next patches.

pkg-initdb should be able to restore pkgmgr database:
 1) for user:
 $ pkg_initdb --uid 5001
 2) globaly:
 $ pkg_initdb

Requires to be submitted with:
 - https://review.tizen.org/gerrit/64351
 - https://review.tizen.org/gerrit/64204

Change-Id: If58d9326c5afcc877ac6ff3ae86924083b764f1c