Toolbar customization

If subfolder "icon" exists, then files named as "0","1","2"...
are used for icons in the bottom toolbar. file "0" to replace the left arrow button, "1" for right arrow button, "2" for the setting button,"3" for the home screen button,...

If a new button is defined (file name "20" exists), uweb also supports VectorDrawable with "android compiled XML" format. All icon files must be either all compiled VectorDrawables or common image formats.

Note: The refresh and tab manager button can not be redefined.