Advanced satellite image cache management

[Korb]

Use case
In cases where a mobile plan is billed per megabyte, or has a low monthly data limit, or in areas with poor mobile coverage, it's convenient to pre-cache satellite images of the desired area when connected to fast and free Wi-Fi. In the current version, this is difficult for a number of reasons: the lack of visualization of tiles in the local cache, the lack of understanding of what scale tiles are already stored in the cache, the lengthy and inaccurate caching process, the inability to clear only the satellite imagery cache...

Proposed Solution

1. Add a feature similar to "Select and save an area" in AlpineQuest Off-Road Explorer.
2. Add the ability to specify a folder for storing satellite image cache.
3. Add the ability to specify the maximum size of the satellite image cache.
4. Add the ability to delete the satellite image cache.

[rusty-snake]

Related: #743