fix: prevent global CSS pollution

[mesqueeb]

@jprodrigues70 this is a commit that tries to prevent some global CSS pollution by changing the CSS names to be more scoped under this package's name.

If you are OK with this please merge into master. But before you release I wanted to do some more work.

Future ideas:

• combine some of the CSS files into 2 file. I think it's a little bit easier to work with the library if we have 1 vue-toaster.css file and one animations.css file. : )
• change stylus to css, to make it easier for many kinds of projects to include this without requiring a build step that handles stylus.

[mesqueeb]

@jprodrigues70 happy new year! did you have any thoughts on this PR?

[jprodrigues70]

thank you!