markupSections function and tests

markupSections takes content that doesn't have enough semantic meaning to form collapsible sections and adds tags/classes to make this work. Works for data from hmrc manuals or the simpler data from the specialist publisher.

markupSections takes:
(1)
<h2>title</h2>
<p>some</p>
<p>tags</p>
<h2>another title</h2>
<p>more</p>
<p>tags</p>

or
(2)
<h2 class="subsection-with-id">
  <span class="subsection-id">HMRCID</span>
  <span class="subsection-title-text">Title</span>
  <span class="subsection-summary">Here is a concise summary of the content</span>
</h2>
<div class="js-ignore-h2s">
  <p>some</p>
  <h2>ignored h2</h2>
  <p>tags</p>
  <h2>ignored h2</h2>
  <p>tags</p>
</div>
<h2 class="subsection-with-id linked-title">
  <a href="#">
    <span class="subsection-id">EIM1234</span>
    <span class="subsection-title-text">Subsection title</span>
    <span class="subsection-summary">Here is a concise summary of the content</span>
  </a>
</h2>

and adds additional html and classes to them so they can be collapsible giving:

(1)
<div class='js-openable manual-subsection'>
  <h2 class='subsection-title'>title</h2>
  <div class='subsection-body'>
    <p>some</p>
    <p>tags</p>
  </div>
</div>
<div class='js-openable manual-subsection'>
  <div class='subsection-body'>
    <h2 class='subsection-title'>another title</h2>
    <p>more</p>
    <p>tags</p>
  </div>
</div>

or

(2)
<div class='js-openable manual-subsection'>
  <h2 class="subsection-with-id subsection-title">
    <span class="subsection-id">HMRCID</span>
    <span class="subsection-title-text">Title</span>
    <span class="subsection-summary">Here is a concise summary of the content</span>
  </h2>
  <div class='subsection-body'>
    <div class="js-ignore-h2s">
      <p>some</p>
      <h2>ignored h2</h2>
      <p>tags</p>
      <h2>ignored h2</h2>
      <p>tags</p>
    </div>
  </div>
</div>
<h2 class="subsection-with-id linked-title">
  <a href="#">
    <span class="subsection-id">EIM1234</span>
    <span class="subsection-title-text">Subsection title</span>
    <span class="subsection-summary">Here is a concise summary of the content</span>
  </a>
</h2>
Add styles for collapsibles  that have been marked up by javascript
Add data-section-id for HMRC manuals and fallback for non-hmrc manuals
Change el to $el as it is a jQuery object
Refactor CSS

- Delete unused CSS
- Tweak padding and add in styles for mobile
Rename classes added by javascript

Add js prefix to classes that are added by JavaScript
- Rename collection-controls to js-collection-controls
- Rename subsection-title to js-subsection-title
- Rename subsection-body to js-subsection-body