Use margin variable

[trumbitta]

Short description of what this resolves:

Just a quick replace of a fixed width margin with the main margin variable for content

Ionic Version: 3.x

[brandyscarney]

Thanks for the PR! A few things here:

1. I'd prefer it if the loading content had a separate variable that was set to the content's margin, since it is a different element.
2. There is a content variable specifically for the ios mode, so we could use this.
3. Can we change all of the modes to keep it consistent?

So something like this:

loading.ios.scss:

/// @prop - Margin start of the loading content next to a spinner
$loading-ios-content-margin-start:      $content-ios-margin !default;

.loading-ios .loading-spinner + .loading-content {
  @include margin-horizontal($loading-ios-content-margin-start, null);
}

loading.md.scss:

/// @prop - Margin start of the loading content next to a spinner
$loading-md-content-margin-start:      $content-md-margin !default;

.loading-md .loading-spinner + .loading-content {
  @include margin-horizontal($loading-md-content-margin-start, null);
}

loading.wp.scss:

/// @prop - Margin start of the loading content next to a spinner
$loading-wp-content-margin-start:      $content-wp-margin !default;

.loading-wp .loading-spinner + .loading-content {
  @include margin-horizontal($loading-wp-content-margin-start, null);
}

[trumbitta]

@brandyscarney thanks for the feedback and the patience. I was at work and in a hurry, so I should have taken my time instead of rushing things out.

Hope the new commit is better than the first one.

[brandyscarney]

Looks great! Thanks for the PR and for making the changes. 😄