fixes #8794

Reported the underlying issue here:
https://github.com/rails/sass-rails/issues/406

Basically `@import` works like this:
* look for the file relative to the current file
* look for the file as an absolute path following the priorities in the
* asset load_paths

If the file can be imported as a relative path that will take
precedence.

So in order to pick up the head and tails inside customization rather
than in app/assets there are three possibilities:
1) use an absolute path. This is not as easy as it seems. There is no
way of indicating a path is meant to be absolute so we would have to
ensure it does not resolve to a relative path.
2) have a application.scss file inside the customization folder. Since
this is the main file it will be used instead of the app/assets one. In
there relative paths will now also default to the customization folder
rather than app/assets. Once we are in an app/assets file though it will
not go back to picking up customization with relative paths
3) use //= require instead of import. rails-sass advices against this as
each required file would be compiled on it's own and variables could not
be shared.

Going with option 1 here:
```scss
// application.scss:
@import "custom/head_import";
```

```scss
// custom/head_import.scss:
@import "head";
```

As long as there is no custom/head.scss in app/assets it will import
head as an absolute path and thus prefer config/custom over app/assets.

This seems like the best option for now as it does not require changes
to the deployments.

We now use the hash of the token for comparison and as the id.
In order to use it you need the original token though. So forms and
thus the session should have token.to_s rather than token.id.

only use the <pre> tag if the response was a text message i.e. during dev errors.
Use the alert-danger class of bootstrap 3 rather than alert-error.

span10 now is .col-??-10.
ul.unstyled now is ul.list-unstyled
also leave out unnecessary li if billing is disabled.

* reran the simple form initializer.
* wrapped submit buttons are now broken and need a fix.
* disabled confirmation validation in client side validations as the
  error message always is attached to the wrong field.