Optimization of fields at export dialog

[Hasenlaeufer]

The handling of fields at export dialog has room of improvements.

Current situation: At export dialog, section "Upload Information", the fields are provided in two groups:

• The first group provides fields used by all infobox templates.
• The second group provides two fields which are used by the infobox templates "Information" and "Object photo": "Source" and "Author". The title of the second group is: Infobox templates "Information" and "Object photo"

The background of the second group: The infobox template "Artwork" provides the fields "Source" and "Author" per file. Therefore these both fields are not provided at export dialog. The title of the second group means: "Not infobox template Artwork".

Potential problem: The visualization is not obvious and might cause understanding problems.

Proposal:

• To make the logic of the second group more obvious, the negation should be avoided.
• The fields of the second group should be provided in dependence of the selected infobox template.
• The visual grouping should be withdrawn.
• The selected infobox template should dynamically determine the provided fields.

The concept of this proposal is similar to the issue "Additional metadata sets #80":

• Show only fields of relevance at the selected context
• Don't show fields without relevance at the selected context

The fields at export dialog should be rearranged. The field order should be the same as at infobox template presentation.

Field labels should be formatted like Lightroom does: with a colon at the end.

[Hasenlaeufer]

Provided by pre-release 0.8.