Trello by default scrolls board contents (lists) horizontally. This can be problematic for boards with a very large number of lists.
This extension allows the user to toggle amongst three display modes - horizontal, vertical, and mixed (tabular/grid layout). This allow easier viewing and editing of boards and lists.
* Removed massive demo folder from the extension, which brings down the size from 2.5MB (!) to 8K.
The reason for this is that the repo contains a "demo" folder with a reasonably big gif file which was not being ignore when generating the extension from the code.
The new command to generate the extension build is `web-ext build -i demo`.
