Customize translation file download

**Is your feature request related to a problem? If so, please describe.**
My self-hosted weblate instance is used to translate informational materials and texts rather than code. When a translation is finished, my users download the finished translations mostly as csv or Excel Open XML. These files always contain the columns:

location | source | target | id | fuzzy | context | translator_comments | developer_comments |  

and the strings are in a random order, or an order I dont understand and have to be sorted to have the correct text for further use. So for the users it is kind of a hustle to extract the translated text in correct order to use it as needed.

**Describe the solution you'd like**
I would like to be able to customize the translation file download, set the order to match the uploaded base file and to select only the columns that are needed.