Fix for 1866
- CLGroup: ensure that the element list has the correct parent set
- CLGroup: allow other Groups to be added as child
- Parser: properly detect whether a group is part of another group
- simplify line ending generation
- RenderInformation need to have an id
- modified to also write the name
- only write name if it is set
- also export at least one global render information (choosing the first one as default)
- correct writing of text anchors
- save plots as PDF file
- Issue 1870: Implemented export of expressions that use the initial concentrations / volumes / values to SBML. For this new global parameters as well as initial assignments so that the dependency chain remains. Only the new global parameter has to be changed to affect the expressions and original model entities.
- compile the model also when exporting to string (so far this was only done when exporting to file)
- display error messages when the model cannot be exported rather than failing silently
- add warning when event assignment target already has an assignment rule, or is not present in th
- removed warning
Undo commits:
  1fe4e7bf6c9ed35d0de962fd83f005bec53bb267
  f7d2a4ba35d6241230d4e29696414c98654936d0
  026af099c2618cef6197005c52da951d14aadbfa