Make Qt5Designer plugin dep optional, use Qt5UiPlugin with >=5.5

CMakeLists.txt

@@ -25,7 +25,6 @@ find_package(Qt5 ${REQUIRED_QT_VERSION} CONFIG REQUIRED
     COMPONENTS
     Core
     Network
-    Designer
     PrintSupport
     Script
     ScriptTools
@@ -37,6 +36,21 @@ if (NOT Qt5Test_FOUND)
   message(STATUS "Qt5Test not found, unit tests will not be built.")
 endif()
 
+find_package(Qt5Designer ${REQUIRED_QT_VERSION} CONFIG QUIET)
+set_package_properties(Qt5Designer PROPERTIES TYPE OPTIONAL
+    PURPOSE "Required to build Qt Designer plugins"
+)
+if(NOT Qt5Designer_VERSION_STRING VERSION_LESS 5.5.0)
+    find_package(Qt5UiPlugin ${REQUIRED_QT_VERSION} CONFIG QUIET)
+    set_package_properties(Qt5UiPlugin PROPERTIES TYPE OPTIONAL
+        PURPOSE "Required to build Qt Designer plugins"
+    )
+    if (Qt5UiPlugin_FOUND)
+        # for some reason, Qt5UiPlugin does not set its _INCLUDE_DIRS variable. Fill it manually
+        get_target_property(Qt5UiPlugin_INCLUDE_DIRS Qt5::UiPlugin INTERFACE_INCLUDE_DIRECTORIES)
+    endif()
+endif()
+
 
 set(REQUIRED_KF5_VERSION "5.7.0")
 find_package(KF5 ${REQUIRED_KF5_VERSION} REQUIRED

designer/CMakeLists.txt

+if (NOT Qt5Designer_FOUND)
+  return()
+endif()
+
 set( oktetadesignerplugin_SRCS
   bytearraycolumnviewdesignerfactory.cpp
   bytearrayrowviewdesignerfactory.cpp
@@ -12,7 +16,11 @@ target_link_libraries( oktetadesignerplugin
   OktetaGui
   OktetaCore
   Qt5::Widgets
-  Qt5::Designer
+)
+target_include_directories( oktetadesignerplugin
+    PRIVATE
+        ${Qt5UiPlugin_INCLUDE_DIRS}
+        ${Qt5Designer_INCLUDE_DIRS}
 )
 
 install( TARGETS oktetadesignerplugin  DESTINATION ${QT_PLUGIN_INSTALL_DIR}/designer )