Resolve the gaps with eclipse UI guidelines

[erwindl0]

Triquetrum 0.1.0 is already compliant with most of the UI guidelines, but there are still some gaps.
The goal is to prioritize them and resolve most of them by the 2017 Spring release.

• 1.7 : no localized resources yet for our own labels and content
• 1.9 : error handling is not yet complete. Most errors get logged via plain logging, but no user notification dialogs yet nor integration with Eclipse logging view.
• 2.8 : icon types follow what is supported in Graphiti. No strict rules yet about SVG icons in Graphiti context bar and other diagram icons can be of different types (i.e. are mostly gifs or SVG, not always png)
• 2.17 : folder/subfolder structure not followed. The very limited nr of icons/images is maintained in one simple folder
• 6.21 : editor & outline are not yet linked, but via the graphical outline one can already quickly jump to a selected position in the diagram
• 6.22 : error/status info not yet shown in the outline
• 7.21 : link between editor tab and package/project explorer selection not yet implemented
• 8 : there is no custom perspective yet

[erwindl0]

1.9 : started using StatusManager etc for error handling, to define UI dialog and/or logging to std Eclipse error log
will now figure out 7.21 first : that was easy, it just works ;-)
next is 6.21

[erwindl0]

6.21 done