Fixed creating of relation
Fixed swap of tables parent-child relationship

When swapping parent-child relationship of table connected with relation
then remove foreign key columns of old child table
Fixed setting foreign keys when tables swapped
Updated issues in Readme, fixed cancel creating relation, fixed adding table

Fixed removing `active` class from tables if creating relation canceled
before finishing it. Fixed add of table if position of table is outside
canvas to set correct position inside canvas.
Toolbar tools moved to standalone folder, added `Generate SQL` blind button