Change Flarum Util slug to Laravel slug

[thanhtaivtt]

Changes proposed in this pull request:

Fix the issue of some non-ASCII characters disappearing from the slugs.

• In the backend I replaced Str Flarum Util to Str Laravel.
• In fontend I have added some UTF-8 variant characters.

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run php vendor/bin/phpunit).

[franzliedke]

Hi, and thanks for your PR!

Fix the issue of some non-ASCII characters disappearing from the slugs.

Could you explain which issue you're referring to? Is there a link where this is explained in more detail?

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Also, please explain the JS changes. Where does that code come from?

[thanhtaivtt]

Hi!

The problem that I encountered is related to converting title to slug in my language (Vietnamese) and some other languages such as Russian, German, French, ... And it was mentioned in issuse #194

My javascript code is developed on gist Slugify makes a string URI-friendly