Define vectors width in nm

[#42153357]

To keep convention that objects inside molecule container specify
their dimensions in nm.
Fix inconsistent image positioning

[#42205787]

Units of imageX and imageY were incorrectly translated. Now they are
specified in nm and handled correctly. Images have the same position
in Classic MW and both Next Gen MW interactives and embeddable pages.
Update conversion tests for images

[#42205787]
Update wrong position of image in MML (!)

[#42205787]

Position of the image in Classic MW was incorrect to provide
workaround for a bug in Next Gen MW. As this bug is fixed, also
position can be set to correct value.