forcing text/html content_type for preview action

(cherry picked from commit a9034f41017d8c660223c80afa16e9aa888cfac7)
Bump to 1.8.5
base class for models

(cherry picked from commit 1fbfb81986668fef82ecc15a128937baebbf1286)
allowing to override admin base controller inheritance via config

(cherry picked from commit 9821e128c2368b0058576dd42cc08e07963b71ec)

Conflicts:
	config/initializers/comfortable_mexican_sofa.rb
Merge pull request #350 from kirel/1.8

Backport: allowing to override admin base controller inheritance via config
Merge remote-tracking branch 'upstream/1.8' into 1.8

Conflicts:
	app/models/cms/block.rb
	app/models/cms/categorization.rb
	app/models/cms/category.rb
	app/models/cms/file.rb
	app/models/cms/layout.rb
	app/models/cms/page.rb
	app/models/cms/revision.rb
	app/models/cms/site.rb
	app/models/cms/snippet.rb
	lib/comfortable_mexican_sofa.rb