[multiview] Add option under PresetSelector to specify whether Chat, TL, or both are opened by default for ChatCell

[FlaminSarge]

Also:
Add Chat+TL button to EmptyCell
Persist Chat/TL mode per cell across refresh if they are ever manually toggled
Display Chat/TL mode on preset previews

Tested pretty extensively:

• Chat/TL mode is represented by 'mode' param, with 0=defaults, 1=chat, 2=tl, 3=both
• As with chat cells, trying to turn off both buttons on the defaults options causes the other to reenable so that one is always enabled
• Selecting a preset layout causes all chat cells in that layout to match the defaults, as presets always omit mode (defaulting 0) for chat cells
• Refreshing the page causes all chat cells to update to the new default if they were left in 'mode 0'
• Setting Chat/TL on a chat cell moves it off of 'mode 0' to whichever it was manually set to, so refreshing the page after this will leave it in that state
• The Chat, TL, and Chat+TL buttons on empty cell create new ChatCells with mode 1, 2, and 3 respectively.
• LayoutPreview shows both icons where it can, shrinking them and then switching them out for the old emoji if shrinking wasn't enough. The old emoji gets a hover title (not a tooltip yet) showing "Chat+TL" on it.

[FlaminSarge]

Considering making mode an enum instead of just a number