Resolve "Allow to create exported file with part of the map"

Closes #537 (closed)

added 4 commits

• d2daa622 - extracting model as a file moved to a proper place
• 2b022463 - tmp file removed after test is finished
• 216cebce - possibility to create submodel with explicitly defined list of elements
• e9e5b8cb - possibility to export part of the map as sbml/celldesigner/sbgnml model from plugin

Compare with previous version

unmarked as a Work In Progress

enabled an automatic merge when the pipeline for e9e5b8cb succeeds

mentioned in commit 6b42f429

merged