Better error handling and user communication on import and export errors

Currently the user only gets a meaningless error message if the import or the export fails.
I see the following possible improvements:

• In the GUI create a simple grid which displays the log entries (of one task only, like the error console in SenchaArchitect)
• In the task grid create an action icon to open / show the above defined log grid
• In the "Add Task" Window use the existing "has error" button also to open the task log grid filtered to show only the errors (or show it directly in the task creation dialog, since normally the popup remains open with an empty body, so here could be listed the info/grid)
• On export errors the task log grid in the task properties window should pop up accompnied by a static error message (that can be removed by closing it)

In addition we will log the taskGUID and taskName on import errors to the log file

Bei fehlgeschlagenem Export: segmentnummer von segmenten mit tagfehlern sollten in der Fehlermeldung stehen
Bei fehlgeschlagenem IMport: Grund für fehlgeschlagenen IMport (wie z. B. vorhandene Änderungsmarkierungen in sdlxliff-files)

Example of errors to be changed:

• Export a Okapi Project with flipped internal tags. This leads to one error in the Okapi Export of that single file. This must be handled sensefully.
• Add a Time measurement to the materialized view complex SQL. When its running to long make a notice.