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