Convert item['slug'] into string before concatenating it with ancestor path.

Fixes #588
Bump act-as-taggable-on to 3.2.6 and include the necessary migrations

Acts-as-taggable-on 3.0 has just been updated to a version that breaks alchemy
builds with PostgreSQL and MySQL. This makes every pull request fail. This is
an attempt to update it to the latest version and see whether with this PR
the Travis builds go through again.

I've tested tagging locally, and it does work as expected with this and Postgres.

Even if this passes Travis: This has to be tested manually; I'm not at all sure
I'm doing the Right Thing here.
Fix typo in README.md.
allow for active model serializer 0.9
v3.0.0
Fixes branches in README. [ci skip]
Fixes a bug where an empty cell elements collection breaks the elements select tag.
Fixes a small icon hover glitch.
Fixes preprocess_image_resize Config option.

The configuration option `preprocess_image_resize` was not compatible with Dragonfly 1.0 syntax.
Allow page names ending in .html
Fix elements updates when there aren't contents_attributes for some content
This fixes a 'When assigning attributes, you must pass a hash as an argument.' error thrown in admin caused by calling content.update_essence() with nil for attributes.
Set transaction names based on page layout in New Relic
Add animated gif support

In admin, use the native image format instead of always converting to
PNG so that users can use and preview animated GIFs
Fix TinyMCE initialization for admin edit pages loaded with Turbolinks
TinyMCE settings are loaded in javascript_pre_init, however this was
previously in <head>. Because Turbolinks is used, scripts in the <head>
are only executed on the first page load or during a page refresh.
Therefore, scripts that change on each page need to be moved into <body>.
To prevent executing shared libraries on each page load,
data-turbolinks-eval=false is added to the main alchemy/alchemy
javascript_include_tag. Alchemy.Tinymce must also not be overwritten if
it's already assigned, because ALchemy.Tinymce.init is defined in
alchemy.tinymce.js.coffee, which is only executed on the first page load.

Conflicts:
	app/views/alchemy/admin/pages/_tinymce_config.html.erb
	app/views/alchemy/admin/pages/edit.html.erb
	app/views/layouts/alchemy/admin.html.erb
Load uncropped pictures directly from CloudFront CDN
This improves performance drastrically by reducing the concurrent load on the Rails backend
Fix TinyMCE initialization when the first loaded page isn't an edit page

Conflicts:
	app/views/alchemy/admin/pages/_tinymce_config.html.erb
Fix TinyMCE initialization - don't use jQuery (not included yet)

Conflicts:
	app/views/alchemy/admin/pages/_tinymce_config.html.erb
Randomize picture CDN hostnames using the upload hash
Fix template cache by removing nil essence types
Fix redirects for pages ending in .html