Add capability to render detailed texture

In comparision with the former orthomgraphic image texture
introduced in 51e1fc602ba2413c364413512a670cee29841611, detailed
texture means texture unit whose coordinate span in rendering
environment can be less than 1 second.

The detailed texture must cover a quard tree node and only read
from one image file named with bottom left coordinate and top right
coordinate info.

Signed-off-by: plysan <plysab@gmail.com>