issue #88

modal WaitDialog introduced for long thread task like
- lock or release
- deleting kassenzeichen
- saving kassenzeichen

By the occasion, many Tasks were reorganised.
Many of them were blocking the EDT. Some GUI-manipulating
tasks were executed outside of the EDT.
The WaitDialog is now shown when the long task SwingWorkers
are executed.
issue #89

login and app initialisation reorganized for readability reasons
Merge branch 'feature/89-main-init' into dev
fixed #90 PluginSupport removed
fixed #90 PluginSupport removed
Merge branch 'feature/90-pluginsupport-removed' into dev