Enable customization of footer links

Run hook SkinMinervaOutputPageBeforeExec to enable to add footer links
in mobile view. To prevent mess up of footer, i created a new hook, so
extensions must explicit use this hook to add links to limited mobile footer.

Bug: 66350
Change-Id: I7bb03d3e79605190874037a54b0fc9052b4e4fc6
Merge "Enable customization of footer links"