Add context what format is being exported to "torro_export_value" filter

[kraftner]

Issue Overview

Currently the torro_export_value filter lacks the context of what format is currently exported but this would he helpful to define different formats for different export formats.

Expected Behavior

One can conditionally filter the export format to e.g. have different formats for export as xls or html.

Current Behavior

You don't know what context this filter is currently run in.

Possible Solution

The filter should receive the $export_format variable from the context it is is run in.

Related Issues and/or PRs

#483