[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
Added more documentation of some methods.
Added tests of the method needsCopiedArchimateElements, prior to
refactoring CopySnapShot class.
Added some more documentation of the CopySnapshot class.
More documentation added.
First checkpoint that sort of does what I want, with objects only. The
code needs to be changed quite a bit still, but I wanted to add this
checkpoint here.
Merge existing references for children to the same container in
snapshot. Untested in all ways.
Comment cleanup.
Seems to handle all "simple" merges, but there are issues with nested
stuff and duplicates.
Merge branch 'merge-on-paste-option-feature' of https://github.com/mbd/archi into merge-on-paste-option-feature