Use a more consistent casing in strings

A lot of strings capitalize the first letter of every word, this isn't used consistently.

Instead, write things normally, only with certain exceptions where certain terms are indeed meant to be like that (e.g. Bluetooth, Wi-Fi, F-Droid)

---

Translations should not cause any issues with this move, translators will be notified (if they watch the project) and the strings are marked as editing and show the diff between the old and new versions. So as long as the meaning doesn't change significantly, it works nicely, at worst you have the translations not have this changed applied. With this said, for safety purposes, I'd recommend merging translations first and THEN this.