qimageinterface fixes, remove old lodepng, address more comments

externals/lodepng/CMakeLists.txt

@@ -1,7 +1,7 @@
 add_library(lodepng
-    lodepng.cpp
-    lodepng.h
+    lodepng/lodepng.cpp
+    lodepng/lodepng.h
 )
 
 create_target_directory_groups(lodepng)
-target_include_directories(lodepng INTERFACE .)
+target_include_directories(lodepng INTERFACE lodepng)

externals/lodepng/LICENSE

@@ -1,21 +0,0 @@
-Copyright (c) 2005-2018 Lode Vandevenne
-
-This software is provided 'as-is', without any express or implied
-warranty. In no event will the authors be held liable for any damages
-arising from the use of this software.
-
-Permission is granted to anyone to use this software for any purpose,
-including commercial applications, and to alter it and redistribute it
-freely, subject to the following restrictions:
-
-    1. The origin of this software must not be misrepresented; you must not
-    claim that you wrote the original software. If you use this software
-    in a product, an acknowledgment in the product documentation would be
-    appreciated but is not required.
-
-    2. Altered source versions must be plainly marked as such, and must not be
-    misrepresented as being the original software.
-
-    3. This notice may not be removed or altered from any source
-    distribution.
-