Show the history of changes for the selected element of diagram/model

[startsevsa]

Often it is important to see what, when and by whom was changed in current diagram/model element.

An realisation example can be taken from other Archi collaboration plugin - DB export/import plugin. Here are some screenshots:

1) Context menu items

2) diagram element history dialog

3) model element history dialog

[janesser]

PR proposal here: https://github.com/archimatetool/archi-modelrepository-plugin/pull/221