cats: adding multiple screens and switching screens on swipe
reintroduce multiple screens picking from commit 3d6733ef Bartosz Golaszewski brgl@bgdev.pl and readapted for linux.
Moved keypad code from main to keypad.c
current screens:
- main
- demo
- keypad
- settings
- developer
Makefile: enable LV_MEM_CUSTOM to fix out of memory error.
Signed-off-by: Francesco Pham francesco.pham@huawei.com