UI Improvements to Workspace Chat

[jaczhi]

Closes #160
Closes #159
Related to #161 (but does not close it because I haven't figured out a way to remove channels yet)

Improvements:

• automatically scrolls to bottom upon entering chat
• enter key sends message (shift+enter for newline)
• prevent sending of empty messages
• messages text now readable instead of white
• added sent time (hh:mm am/pm) in addition to date
• profile pictures are now 1) deterministic across users/devices, 2) different for each sender, can differentiate people by their PFP
• prettified top navigation bar and buttons
• use memos instead of functions for improved rendering efficiency
• new UI and logic to create a chat channel
• chat channels are no longer hardcoded (other than '#general' to avoid user confusion)

New look:

[jaczhi]

I updated this PR; I added custom chat channels functionality

[markverick]

I tested your PR; Everything you described looks good to me.