Fix media link classes not being added

[RudeySH]

I noticed this when using both the Bootstrap extension and the Media Links extension. When Bootstraps adds img-fluid, the Media Link extension didn't add their classes as well. This PR should fix that.

[RudeySH]

Tests are failing because the class attribute is now appearing before the width and height attributes. I've already fixed this in TestMediaLinks.cs but I just noticed MediaSpecs.md and the unit test file that appears to get generated by that markdown file. When modifying these Specs .md files, how do I regenerate the *.generated.cs file along with it?

[MihaZupan]

There is a SpecFileGen project in the solutuion. Running that will regenerate the test code

[MihaZupan]

Can you also add a test case to emphasize the specific case this PR is fixing

[RudeySH]

The thing is, the Bootstrap extension adding img-fluid to embeds doesn't actually make sense. I'll add some tests but they'll have to be changed if #434 gets resolved.

[RudeySH]

I'm currently running into nunit/nunit3-vs-adapter#691 and I'm unable to run most tests in Visual Studio. I'll commit them but I have no idea if they'll pass, I guess we'll see.

[MihaZupan]

Does it work if you run them from the command line with dotnet test?

[RudeySH]

That works, thanks. It seems they pass!