add ui target

src/ui/CMakeLists.txt

@@ -0,0 +1,7 @@
+# UI source files are listed here as they are added.
+# Append headers and sources to HDRS and SRCS in PARENT_SCOPE,
+# following the same pattern used by src/lib/.
+#
+# When this directory has actual sources, the parent CMakeLists.txt
+# must be updated to convert DotaFactory_ui from an INTERFACE library
+# to a regular static library (and enable AUTOMOC on it).