Add two features

[Hui-Li]

Add two features:

1. Use JQuery to sort conferences. The order of conferences in conferences.yml does not affect how they are shown on the web page now. utils/process.py is not needed anymore.
2. A conference can have multiple types now. Multiple types can be set in conferences.yml:

sub: 
    - DM
    - IR

Original one sub per conference is still supported:

sub: DM

Check the Demo. The The Web Conference 2021 has two types.

[abhshkdz]

Perfect, thank you!