Extension:CentralNotice/Banner mixins (deprecated)

Introduction
A banner mixin is a piece of supporting javascript, stylesheets, or PHP which can be reused by many banners. At the moment, there are three types of code you can integrate using mixins:


 * Preload rule : a javascript snippet that is executed to determine whether to continue loading the banner.
 * Calculated variables : PHP functions which substitute dynamic values for placeholders, formed using triple-braces e.g., "" . These functions can take arguments, given like "".
 * JS and CSS : a bundle of code loaded using MediaWiki's Resource Loader.

An example of each would be, respectively: banner cookie diet; daily and cumulative amount thermometer; and dropdown donation form logic. A single mixin may be implemented by any combination of these methods.

List of available mixins

 * BannerDiet : Basic cookie-counting scheme which will limit the number of times a viewer sees banners from each group. Operation is dependent on two variables, "hide-cookie-name", which defines the group that the banner belongs to, and "hide-cookie-max-count", which is the maximum number of times a person should see the banner.

Writing mixins
Mixins are deployed along with CentralNotice source code. Since they can affect many banners, we get the warm fuzzies thinking that these snippets are receiving proper code review.

If you have a new mixin to propose, the fastest way to get attention is to push a CN patch for review.