Revert "remove deprecated gems 'jekyll-page-hooks' and 'jekyll-date-format'"

This reverts commit 181d620c1c46c644c4319e81edc342ae5a30c067.
Support octopress-hooks and octopress-date-format #1622
Use `octopress-hooks` and `octopress-date-format`

Not applied in 73e540409ceb8bc18048b6a96a4b815fc303ea28.

Fix #1622.
Merge pull request #1628 from yous/patch-octopress-filter

Use `octopress-hooks` and `octopress-date-format`
Set layout to null to avoid page defaults.
Set layout to null to suppress warning

Not applied in 0f1660437beba58cd2974f07270b19305b9bbfd9.
Merge pull request #1629 from yous/patch-layout

Set layout to null to suppress warning
Merge branch 'master' of git://github.com/imathis/octopress into source
Update from octopress head