OS Features - Extension Edition wót Lastie

Adds new features and themes to Online Sequencer!

Sequencer features include:
- AdBlock
- MultiSolo (has been added to main site, but will keep for OS Rooms)
- Slider Text Inputs
- And a BPM tapper.

Chat features:
- Midnight Rose theme
- Image auto hider
- Chat user blocker
- Chat name stylizer (fixed!)
- And link embeds

Themes:
- Midnight rose chat theme

Account Management:
- Adds a drop-down for easy account-swapping

Also adds a small fix to the forums page allowing the chat popup to work.