[Accessibility] Other miscellaneous issues

[SushantKafle]

• Screen reader reads the user-avatar and the name in the chatbox, redundantly.
  
  Solution: One solution is to use "aria-hidden" to indicate the screen readers to skip reading the avatars.

• The "Event type" dropdown menu (in https://virtual.acl2020.org/schedule.html) is a multi-select menu but SR doesn't tell which ones are selected.
  

• Screen reader reads the calendar links below each paper weirdly. For instance in (https://virtual.acl2020.org/paper_srw.58.html), Square brackets are read explicitly, e.g., square bracket open google square brack close. It would be nice to have them be read as a single unit: just "Google".
  

[anaerobeth]

• Screen reader reads the calendar links below each paper weirdly. For instance in (https://virtual.acl2020.org/paper_srw.58.html), Square brackets are read explicitly, e.g., square bracket open google square brack close. It would be nice to have them be read as a single unit: just "Google".

@SushantKafle I added aria-hidden="true" to the spans containing the brackets. If you would like to test the referenced branch with those changes to confirm they work with various screen readers, I'll be happy to open a PR. Thanks.

[hao-fang]

@anaerobeth Let's add your changes. I think it is a good move. Thanks!