Header Changes & Tweaked Login Logic
Header Changes & Tweaked Login Logic

- [x] Simplified Legacy Login Logic
- [x] Changed Legacy Login Logic to try v2 login first, which most newer models will use, and only fallback to v1 login if v2 login fails (signaling the router is likely an older model).
- [x] Removed unnecessary `Connection` header

These are currently untested changes, but I suggest we keep the `Cache-Control` header for all calls to avoid possible false-positives for `device_tracking` functionality
balloob/pynetgear