Stairs

Stairs can be produced with jpseditor

Assuming that:

• stair is a subroom between two horizontal subrooms. These two subrooms have two different elevations
• the subroom is of type Stair (uppercase/lowercase not relevant)

The plane coefficients of the stair are then calculated using @osterkamp1 formula!

New in this MR:

• (horizontal) Rooms have an elevation that can be set via GUI.
• Crossings separating two rooms, inherit the elevation of the room which is not a Stair. This assumes of course that a crossing separating two stairs does not exist.
• Name of rooms and obstacles are updated in the GUI by pressing enter.
• Change of the elevation is also by pressing enter
• If room's elevation changes (e.g. during editing), then the crossing's elevation changes too.