Add MDN to list of sites using Pipeline

https://github.com/mozilla/kuma/pull/3580

Fixes #497.

Fix for wrapping javascript code.

Typo in installation.rst

Safely concatenate JavaScript

Fix shadons on finders

add templates to test pipeline

Fixed recursive call to django's staticfiles.finders.find() to prevent Exceptions on missing files with 3 extensions.

Fix for #329.

Most JavaScript packages wrap their code in IIFEs, which is good.

Pipeline used to concatenate JS only with a newline. That can break those IIFES
though:

    (function() {
      // package A
    }()) // No semicolon! Most people put one here, but unfortunately not all!
    (function() {
      // package B
    }());

The above is equivalent to:

    (function() {
      // package A
    }())(function() {
      // package B
    }());

Suddenly we have a function call!

With this commit, JS is concatenated with a newline followed by a semicolon,
which fixes the above issue:

    (function() {
      // package A
    }()) // No semicolon! Most people put one here, but unfortunately not all!
    ;(function() {
      // package B
    }());

There is no need to worry about superfluos semicolons, such as:

    (function() {
      // package A
    }());
    ;;(function() {
      // package B
    }());

That is still valid JavaScript and the extra semicolons will be removed by the
minifier.

Just a typo

add econding to open

Add max_length arg to PipelineStorage.get_available_name.