[CSV Import] Add new Selected Model Import Handler

* This Import Handler works on selected models, rather like the Export Handler
[CSV Import] Import CSV files
[CSV Import] Use try/finally to close parser
[Help] Remove appendix

* Acknowledgements are in situ
[CSV Import] Update changes.txt
Merge branch 'csv-import'
The "Select All" action is enabled on the Model Tree, Visualiser and Navigator