Updated hacking instructions.
Update docs/ theme
Removed dead declarations.
Simplified selectors.
Make input button styling available for btn classes too.
Adapted UI elements in preparation for more page types.

Class-based generic views have been used for this, since functionality
will be mostly shared by other types of pages. Small bits might still be
missing, but will be reviewed as part of bug 2866.

Fixes bug 2865.
Fixed template path.
Moved intra-field validation to models.
Set explicit field ordering.
Implemented generic page display.
Rather extend the base template.
Use a more meaningful id.
Moved URL to the abstract page model definition.

The redirecting functionality will be shared by pages.
Reworded title and help text.
Removed `display_on_register` field.

Legal pages imply this functionality.
Fixed URL generation.
`get_absolute_url` can be shared across page types.
Ignore current page when checking for existing virtual paths.
Implemented even more generic static page views.

Create/Update views will be built according to the type of page set in the
url pattern.
Use more sensible names for templates.