TODO:
- [x] More universal Makefile
- [ ] Check and fix registration and login
- [x] UI: destroy child elements everywhere
- [x] use parent widgets pointers to count the margins correctly
- [ ] Hotkeys for buttons
- [ ] Group elements as lists
- [x] Process arrows
- [x] Optimize modals re-drawings
- [ ] Bug with file list on downloading files
- [ ] Remember page numbers
- [ ] "Server message" to notification
- [ ] file list -> list template

UPLOAD:
- [ ] Progress bar
- [ ] Show notifications and messages from the server (universal way)
    use notification or something