Though we consider the "room list" to mean the RoomList component specifically, the room list is actually the entire left panel as far as the user is concerned.
The new proposed designs for the room list modify the whole left panel, so we had might as well break it into new and old now instead of later. This "new" left panel is a bare-bones implementation and meant to only provide the absolute basic feature set to function for those who enable the experimental room list, for whatever reason. This is not intended to be a final implementation, or even remotely close to what it could be. An example of this is the lack of breadcrumbs. Given they are likely to change, they are excluded from this temporary skeleton completely.
This also includes a purple/pink bar between the tag panel and left panel. This is so we can, if needed, differentiate between people who made the mistake of turning on the experimental room list while the overall aesthetic makes it indistinguishable. Once the designs are moderately approved, we can (and definitely should) remove the hideous indicator.
This does a number of things (sorry):
* Estimates the type changes needed to the dispatcher (later to be replaced by https://github.com/matrix-org/matrix-react-sdk/pull/4593)
* Sets up the stack for a whole new room list store, and later components for usage.
* Create a proxy class to ensure the app still functions as expected when the various stores are enabled/disabled
* Demonstrates a possible structure for algorithms
