Feature Request: Low-bandwidth / Metered mode

**Is your feature request related to a problem? Please describe.**
This is admittedly a pretty niche need, but I'm hopeful it will also be easy to implement and therefore worth it for the minor benefit. I'm currently in a situation where my phone is my only internet connection, and I'm in an area with pretty poor reception, so it's also pretty slow. This means it's ideal for me to keep unnecessary data use down to a minimum, both to extend how long before I hit my full-speed cap and start getting throttled and to keep things as speedy as possible.

I was just going through updating my apps, and every time I'd open an app page in Droid-ify to update it, the screenshots would load. Sometimes they would load before I started the update, and so they would be fully loaded by the time it started downloading, and sometimes they wouldn't. In the latter case, they would take a very long time to load, sometimes not even finishing by the time the download finished (and that takes a while). This is because the bandwidth is so limited it was struggling to download the update and the images simultaneously, and doing so not only slowed the already slow downloads down even more, but wasted bandwidth.

**Describe the solution you'd like**
What would be nice would be an option in settings to activate a low-bandwidth mode. Whether this would be a simple on/off toggle or it would have more configuration settings under it is something that would need to be determined, but at the very least it should prevent the loading of screenshots when accessing an app page from the updates (and probably installed) tab(s), since they're not necessary at that point, like they are when browsing apps. If that's not possible, or if it's easier to just always block them, then it could do so regardless of what tab you're in.

**Describe alternatives you've considered**
Not quite as good, but there could also be a pop-up menu when long-pressing an app in the update tab with an update option. Once Issue #20 is implemented, it would also provide a similar solution, though either of these aren't quite as good because you can't open a page to see what's new in the update. This is pretty minor, though, so I only make this suggestion in case it would be easy to implement; if not, I'd say it's not worth it.