Rename lazy-url option data attributes

This commit renamed the lazy-url-horizontal and lazy-url-context data
attributes to lazy-horizontal and lazy-context. It's shorter and makes
more sense.

See related commit and discussion:
https://github.com/causes/replacejs/commit/f1f09f1c10ee8cc05543cad468b484fe5631b436#L0R166

Change-Id: I19f5efc05b05ee0ea3cb260f24bac18eca8a9c37
Reviewed-on: https://gerrit.causes.com/26502
Reviewed-by: Nebojsa Petrovic <nebs@causes.com>
Tested-by: Nebojsa Petrovic <nebs@causes.com>