Add tests for ignoring properties case for ordering. Related to #78

[Astrael1]

Hello :)
There are some issues with #78

1. Shorthands
   I don't know how the plugin should behave with shorthands. I assumed that if user types

Border-width: 1px; Border-top-width: 2px;

they do it on purpose and they expect it to behave just like any other css properties. Do you agree with that?

2. It needs postcss-sorting to have an option to ignore case. Shall I report that issue there?
3. Do you have any more tests ideas? Are you willing to merge the tests without other changes?

[hudochenkov]

1. Shorthands area already supported

   stylelint-order/rules/checkAlphabeticalOrder.js

   Lines 11 to 19 in 416d00c

   	// OK if the first is shorthand for the second:
   	if (isShorthand(firstPropData.unprefixedName, secondPropData.unprefixedName)) {
   	return true;
   	}
   	// Not OK if the second is shorthand for the first:
   	if (isShorthand(secondPropData.unprefixedName, firstPropData.unprefixedName)) {
   	return false;
   	}

   I don't expect anything new needed for this.
2. Correct. First postcss-sorting need to ignore case, then we can add it to stylelint-order. Because postcss-sorting powering autofixing, it would be strange if logic for checking order in stylelint-order would be different than its fixing functionality.
3. I've added few suggestions. Also need tests for properties-order.

[Astrael1]

@hudochenkov I need your decision on this. User may provide above properties. In this case they should be informed, that the plugin doesn't work like that.

[Astrael1]

I added some tests. I haven't added tests in grouped-strict yet.

I'd like to know if it's fine. Are there too many tests or not enough etc?

[hudochenkov]

I haven't added tests in grouped-strict yet.

They are not needed.

[hudochenkov]

Thank you!