Move wgt-backend implementation from app-installers
Requires to be submitted with:
- https://review.tizen.org/gerrit/#/c/54291/
Aligned with app-installer's commit:
532a4707928d6d137c2cb93ae3523f25f0ac06ee
Change-Id: I30347bd6ca66026d3e363bb16000a44e2d791f39