[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
Adds support for a replace-in-names operation.
This puts an action on the context menu for a diagram, that is
enabled, if the selection contains "stuff" that can have its names
changed. The implementation is rough, and e.g. does not have a proper
"search and replace" dialog, but simply asks the user for input twice.
Merge branch 'find-replace-in-name-feature-v2' of https://github.com/mbd/archi into find-replace-in-name-feature-v2