Fix issues with watching CSS reloading

[rodrigogiraoserrao]

This will close #2063.

The only reason I am a bit confident in this fix is because all the tests pass.
I am not 100% sure why this works, but I have a conjecture: the call to reset_styles was flagging the need to repaint a widget too soon and it was either preventing the latter refresh from happening or it was keeping some outdated information around.

I got to this conclusion because setting the border property programmatically works, and the code that runs in that case is just the __set__ in the descriptor and the layout refresh, as opposed to what happens when the CSS is reloaded, which runs many more lines of code, so I figured that the CSS reloading was “doing too much work”.

Note: Playing with the code and running the tests suggests we can actually get rid of the method reset_styles altogether.

[willmcgugan]

That may be right. I'm assuming you've pushed the hot reloading quite hard and can't break it.

If that method isn't called anywhere, then I'd go ahead and remove it.

[rodrigogiraoserrao]

I'm assuming you've pushed the hot reloading quite hard and can't break it.

I'm going to go ahead and add tests for the hot reloading.

[willmcgugan]

@rodrigogiraoserrao Still working on those tests?

[rodrigogiraoserrao]

@rodrigogiraoserrao Still working on those tests?

Yeah, there wasn't a good way to test the hot reloading and take a snapshot test.
Wrapping up now.

[rodrigogiraoserrao]

@willmcgugan now I'm happy.