ftk/font: fix freetype cache size bug

NOTE:
when using freetype font engine, the fonts size is not same, for example,
when setting font size to 38, some font's actually size may be 38x35, while
some may be 39x37. in order to cache all these irregular font, we need a
larger font cache size for each font.
widget: strength tabpage
widget/tab: add tab_width/height setting

clean code in demo_tab.c
fix font bug "Bus error" on ARM board

caused by d8a5e623598035405202aed2d38a6388def1182d