This PR refactors the configuration parser, replacing the old parser implementation with a new, more structured approach that includes validation and improved organization.
Key changes:
- Complete rewrite of the configuration parser using a map-based structure with built-in validation
- Addition of comprehensive validator functions for configuration values
- Renamed numerous configuration getter methods for better consistency
Some Miniflux clients expect a specific version format.
For example, Flux News converts the string version to an integer.
Using `Development Version` will break some clients.
There is no need to specify `class="icon"` on al svg icons, as all svg are used
as icons anyway. But just in case, let's specify this in the css only for svg
directly under `a` and `buttons`, to be on the safe-side.
For example, seeing "Next check: 14m56.245483933s" in feeds list after force-refreshing a feed.
This rounds to the nearest second, so it'll instead be "14m56s"
Other examples from latter two test cases:
- "12.345678s" -> "12s"
- "1m27.654321s" -> "1m28s"
