Change TagBuilder Attributes and HTML Helper dependencies to be case insensitive.

- This involved adding the StringComparer.OrdinalIgnoreCase comparer to the TagBuilder's Attributes dictionary.
- Added tests to validate that all methods that made use of TagBuilder.Attributes abide by the new ignore case mechanic.
- Added two sets of tests to validate the new functionality of Object => Dictionary HTML helper tests.
- Modified a functional test that utilizes HTML Helpers to provide same attribute-different case objects.
- Fixed existing HTML helper tests to account for new ordering of attrbutes (dictionary no longer adds key value pairs, it sets them).

#1328