TODO:
- [x] More universal Makefile
- [ ] Draw only when something changes in UI
- [ ] 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
- [ ] Simpler refresh on typing / entering in input
- [ ] Group elements as lists
- [ ] Process arrows
- [ ] active_id -> просто указатель на элемент

INPUT:
- [ ] hidden text for passwords
- [ ] move cursor through the text in input