Proper Unicode Support for Tags

[Robert Jäschke]

Apparently, not all Unicode characters are allowed as tags. For example, the character 😃 (SMILING FACE WITH OPEN MOUTH) can not be added as a tag.

Steps to reproduce:

1. Edit a post and add 😃 as a tag.
2. Save the post.
3. Edit the post again (or go to https://www.bibsonomy.org/tag/😃)::) the tag has disappeared (and the post is not listed on https://www.bibsonomy.org/tag/😃)..)

There's also a problem with the JavaScript tag editor (when adding tags in the post list): it accepts the tag and adds it to the HTML page but after a reload the tag is gone.