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Resolve "wrong start and end of reaction lines"

Closes #812

See merge request !771

when exporting reaction to sbml unnecessary colinear points are removed so imported model has different lines

when exporting to SBML unnecessary lines are removed, so after deserializing set of lines is different

when reaction line was short (1 segment) and there was need for operator in product/reactant side the layout was regenerated

Resolve "Custom images as overlay levels  or background"

Closes #487

See merge request !768