* Fixed "Cursor Positions on Shared Whiteboards are Inconsistent".
The main fix is in the method cursor_point_to_space in
public/javascripts/spacedeck_whiteboard.js.
The calculation of the coordinates of the mouse pointer from absolute
window to the whiteboard space coordinates was incorrect.
There were a number of dependencies on this method which were updated
as a result.
One side-effect was that the div for the lasso tool needed to be
moved inside the div for the whiteboard.
* Fixed minor panning calculation problem. Works now!
* The MongoDB/Mongoose data storage is removed in favor of Sequelize. This abstracts over SQLite or RDBMs like PostgreSQL and MSSQL. The default is SQLite, which significantly simplifies deployments in end-user environments.
* As Spacedeck now has no more mandatory server dependencies, we can wrap it in Electron and ship it as a desktop application.
* Removes docker-compose.yml
* First version of import UI
