fix(item): fix color input for item divider and list header

[brandyscarney]

• adds ItemDivider class to add color and mode css classes to item
  divider
• adds e2e test for item divider colors
• adds sass variables to improve control over list headers and item
  divider styles
• fixes style for item divider so it will be styled regardless of being
  inside a list for md and wp modes
• item divider and list header now get their own classes for colors
• change the default text color and background color to match the theme
  variables. This makes popover look better on dark theme and removes the
  nesting of styles that breaks list headers.

Snapshot for these changes: http://ionic-snapshot-go.appspot.com/ionic2/snapshots/tt8/v2m/chrome_400x800

e2e test added to snapshot for item divider: http://ionic-snapshot-go.appspot.com/ionic2/snapshots/v2m/chrome_400x800#41fcb91b

fixes #8376

[gigocabrera]

@brandyscarney the latest nightly build fixed the issue. However, when I try to apply global SCSS overrides for the button color and the text color, they are not being applied anymore

// Navbar custom styles
// --------------------------------------------------
$toolbar-ios-button-color:   #31C0E6;
$toolbar-md-button-color:  #31C0E6;
$toolbar-wp-button-color:   #31C0E6;
$toolbar-ios-title-text-color: #fff;
$toolbar-md-title-text-color:#fff;
$toolbar-wp-title-text-color: #fff;

[brandyscarney]

Hey @gigocabrera. :) I'm not able to reproduce that using the conference app. Are you applying color to the button? If you have a color on the button it won't take the default. Otherwise, could you create an issue with the markup you are using so I can reproduce it? Thanks!

[gigocabrera]

@brandyscarney my bad. This works as expected. I was looking at the wrong thing 😜