Improve 'default application' handling

Problem

If no default application is defined, the last used application will be used to open a file on activation. E.g. for pictures this might be annoying when opened with some graphic editor from time to time.

The current best practice is, to select open with --> other application and check the "default application" box in order to define the default to use. However that is kinda hidden. For some users it is not clear that this step is required.

Proposed Solution

1. If there is no default application set for a specific mime type, and the "open with" menu is used, the default will be set to the selected application.

2. Like 1. but some dialog would ask if that application should be used as default.

3. An additional item in the "open with" menu: "set default application". That would open the same dialog than "open with other application", but with "use as default" pre-selected.

I would go for 1. and 3. ... and optionally add 2. later on if someone complains.

Critics / Suggestions ?

Edit: As well it would help to highlight the default application in the list in some way, so that it is more clear that this application will be used per default. To be first of the list of "preferred applications" imo is not sufficient. Maybe a separate tree-headline "Default Application" would be good.