[INFRA] Performance tests improvements

[tbouffard]

The following propositions have emerged during #856 developments

• also run tests with the model-complete-semantic.bpmn file. It is larger than B.2.0. However, as it size changes each time we support new BPMN elements, it may be hard to understand performance change, but it would also detect issue if new supported BPMN elements has performance impacts
• load tests: add tests for
  • no fit on load
  • fit center as the implementation also translates the diagram in addition to fit management
• remove code duplication in statistics generation
• data - put it in human readable format
• find way to identify set of tests (data, branch, short comment)
• run on other browsers: firefox ([INFRA] Investigate how we could run tests with Firefox #916) and safari ([INFRA] check the testing possibilities for the Safari browser #876)