Expressions should be shown similar to data formats in the config panel

[lhein]

The current implementation of the expression editor requires users to open up a dedicated expression editor window to configure the expression. This is complicated for users to use and also to detect the configured values easily.

Suggestion:

• Embed the expression editor's fields analog to what has been done for data formats (for instance in Marshal step) directly in the config panel
• Preset "Simple" as the default selected expression language

This way the user can see and edit the values directly and more easily.