Add configurable movement keys

[tahminator]

Summary

Allow movement keys (usually h/j/k/l) to be configurable by user instead

Note

arrow keys still work the same way, allows for movement and cannot be changed

As for why: I built a bad habit of swapping j and k wherever I use Vim bindings and so this feature would be very helpful to me. I'm honestly not sure how many other people would benefit from this other than me, but I figured I'd put up a PR in case you would like to make this a feature 😄

Testing

All tests passing:

$ cargo fmt --all
cargo clippy --no-default-features --features telemetry -- -D warnings
cargo test --no-default-features --features telemetry

    Checking spotatui v0.39.1 (/Users/tahminator/personal/github/spotatui)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.91s
   Compiling spotatui v0.39.1 (/Users/tahminator/personal/github/spotatui)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 2.07s
     Running unittests src/main.rs (target/debug/deps/spotatui-fd2c712806c22bd7)

running 253 tests

// ...

test result: ok. 253 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.80s

I have also been dogfooding the changes for the past day, haven't noticed anything broken

Additional notes