Add ENGLISH title and short/long descriptions to metadata folder

[trikaphundo]

Fixes #390 .

Descriptions were copied from the F-Droid's repositories data and data-localizations.

1. Only the short_summary.txt can be translated in Weblate.
2. The full_description.txt cannot be translated in Weblate; hence the impossibility to show it translated to users on your app's page in F-Droid and Google Play, as stated in Add metadata to make F-Droid and Google Play pages translatable #390 .

Notes

From F-Droid's page about metadata.

Please be aware that texts in the app’s metadata file will override all other descriptive texts provided through the structures explained below. This affects Name, Summary, and Description. Once metadata fields that were previously in the metadata file have been moved to the app’s source repo, please file a merge request or issue to remove Summary and Description from the app’s metadata file.

1. Changes in this PR, and their future PR translations, will not be visible for the users until you demand F-Droid explicitly to remove the short and long descriptions from their repositories (linked in first paragraph).
2. Before doing so, you should retrieve and save the already existing translations of the short summary: the ones in Weblate. They can be easily copied directly from the Weblate link I provided above, from the tab "Other languages".
3. For those languages that have a short summary translation (point 2), you should provide the full description in English; since short and full description files are mandatory for F-Droid.

[wolpi]

Thanks!
Let's see how store pages evolve ...