Maintenance: translation files

[wutschel]

With the latest changes to use Weblate for the translation maintenance it became obvious that several text segments are double defined and several are not existing or translated for all languages yet. To be able to maintain the languages it is desirable to have the English translation as the reference and derive the other languages from this as done in #380.

What needs to be done:

• Keep "More (%ld)" and remove "More (%d)"
• Keep "%d results" and remove "%lu results"
• Keep "enjoy!" and remove "Enjoy!"
• Add "Last Updated: %@" to the English file
• Add "Username" to the English file
• Add "Never" to the English file
• Add "Not Available" to the English file
• Add "Copy to clipboard" to the English file
• Remove "Pull to refresh..."
• Remove "METHOD\n%@\n\nPARAMETERS\n%@\n"
• Remove one (of two) instances of "Music Add-ons"
• Remove one (of two) instances of "Video Add-ons"