Refactor presence event code in examples

[chacha912]

What this PR does / why we need it?

• Use 'presence' event instead of 'my-presence' or 'others' when displaying online clients
• Remove unnecessary code in quill example
• Display remote cursors when client connects to document (quill, codemirror)
• Modify selection color to be set by presence(codemirror)

Any background context you want to provide?

What are the relevant tickets?

Fixes #

Checklist

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

Merging #614 (ec094a4) into main (53185d5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #614   +/-   ##
=======================================
  Coverage   87.69%   87.69%           
=======================================
  Files          81       81           
  Lines        8205     8205           
  Branches      816      816           
=======================================
  Hits         7195     7195           
  Misses        700      700           
  Partials      310      310           

[hackerwins]

@chacha912 Thanks for your contribution.

Should we change the base to v0.4.5-example like in #590 so that it doesn't deploy to https://yorkie.dev/examples?

[chacha912]

@hackerwins I modified the examples in the "public" folder, so I think we can merge to main.
If modifications are needed in the v0.4.5-example branch, I will add commits accordingly.