Add kra and ora imageio plugins (read-only)

kra is the native format for Krita and ora the interchange format
for krita, gimp and mypaint (it's also mypaint's native format).
Both formats are simply zip containers with an embedded png.

REVIEW:126675

CMakeLists.txt

@@ -20,6 +20,12 @@ include(CheckIncludeFiles)
 set(REQUIRED_QT_VERSION 5.3.0)
 find_package(Qt5Gui ${REQUIRED_QT_VERSION} REQUIRED NO_MODULE)
 
+find_package(KF5Archive)
+set_package_properties(KF5Archive PROPERTIES
+    TYPE OPTIONAL
+    PURPOSE "Required for the QImage plugin for Krita and OpenRaster images"
+)
+
 # EPS support depends on the gs utility; non-UNIX systems are unlikely to have
 # this available in PATH
 set(BUILD_EPS_PLUGIN FALSE)