Package actions now have a separate box on the package details page. Add
a package merge link in that box.

Link leads to a new page (pkgmerge.php) that can be used to confirm package
merging. A separate page with confirmation is used to avoid CSRFs.

Signed-off-by: canyonknight <canyonknight@gmail.com>
Signed-off-by: Lukas Fleischer <archlinux@cryptocrack.de>