CMake: overhaul and improve scripts

- Bump minimum required version and
make use of more modern language features
- Rely more on target_...() commands to establish dependency
relationships between targets rather than directory property commands
- Improve libtorrent package discovery
- Enable and handle application features more explicitly
- Improve user-facing output
- Fix various compilation issues on Windows (MSVC and MinGW) and macOS
- Improve handling of translations
- Add explanatory comments where relevant
- Make CMake scripts fully independent of qmake files/details
- Remove old functions/macros

src/gui/CMakeLists.txt

@@ -1,6 +1,3 @@
-set(CMAKE_AUTORCC True)
-set(CMAKE_AUTOUIC True)
-
 add_library(qbt_gui STATIC
     # headers
     aboutdialog.h
@@ -80,7 +77,7 @@ add_library(qbt_gui STATIC
     uithememanager.h
     updownratiodialog.h
     utils.h
-    
+
     # sources
     aboutdialog.cpp
     addnewtorrentdialog.cpp
@@ -180,6 +177,7 @@ add_library(qbt_gui STATIC
     rss/rsswidget.ui
     search/pluginselectdialog.ui
     search/pluginsourcedialog.ui
+    search/searchjobwidget.ui
     search/searchwidget.ui
     shutdownconfirmdialog.ui
     speedlimitdialog.ui
@@ -188,33 +186,9 @@ add_library(qbt_gui STATIC
     torrentcreatordialog.ui
     trackerentriesdialog.ui
     updownratiodialog.ui
-
-    # resources
-    about.qrc
 )
 
-if (WIN32 OR APPLE)
-    target_sources(qbt_gui PRIVATE programupdater.h programupdater.cpp)
-endif()
-
-if (UNIX AND Qt5DBus_FOUND)
-    target_link_libraries(qbt_gui PRIVATE Qt5::DBus)
-
-    target_sources(qbt_gui PRIVATE
-        qtnotify/notifications.h
-        qtnotify/notifications.cpp
-    )
-
-    find_package(X11)
-    if (X11_FOUND)
-        target_sources(qbt_gui PRIVATE
-            powermanagement/powermanagement_x11.h
-            powermanagement/powermanagement_x11.cpp
-        )
-    endif()
-endif()
-
-target_include_directories(qbt_gui PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
+target_sources(qbt_gui INTERFACE about.qrc)
 
 target_link_libraries(qbt_gui
     PRIVATE
@@ -223,13 +197,36 @@ target_link_libraries(qbt_gui
         Qt5::Gui Qt5::Widgets
 )
 
-if (APPLE)
-    target_sources(qbt_gui PRIVATE macutilities.h macutilities.mm)
-    find_package(Qt5 ${requiredQtVersion} REQUIRED COMPONENTS MacExtras)
-    target_link_libraries(qbt_gui PRIVATE Qt5::MacExtras objc)
+if (DBUS)
+    target_sources(qbt_gui PRIVATE
+        qtnotify/notifications.h
+        qtnotify/notifications.cpp
+        powermanagement/powermanagement_x11.h
+        powermanagement/powermanagement_x11.cpp
+    )
 endif()
 
-if (WIN32)
-    find_package(Qt5 ${requiredQtVersion} REQUIRED COMPONENTS WinExtras)
-    target_link_libraries(qbt_gui PRIVATE Qt5::WinExtras PowrProf)
+if ((CMAKE_SYSTEM_NAME STREQUAL "Windows") OR (CMAKE_SYSTEM_NAME STREQUAL "Darwin"))
+    target_sources(qbt_gui PRIVATE
+        programupdater.h
+        programupdater.cpp
+    )
+endif()
+
+if (CMAKE_SYSTEM_NAME STREQUAL "Windows")
+    target_link_libraries(qbt_gui PRIVATE
+        Qt5::WinExtras
+        PowrProf
+    )
+endif()
+
+if (CMAKE_SYSTEM_NAME STREQUAL "Darwin")
+    target_sources(qbt_gui PRIVATE
+        macutilities.h
+        macutilities.mm
+    )
+    target_link_libraries(qbt_gui PRIVATE
+        Qt5::MacExtras
+        objc
+    )
 endif()

src/gui/rss/articlelistwidget.cpp

@@ -33,7 +33,7 @@
 #include "base/global.h"
 #include "base/rss/rss_article.h"
 #include "base/rss/rss_item.h"
-#include "uithememanager.h"
+#include "gui/uithememanager.h"
 
 ArticleListWidget::ArticleListWidget(QWidget *parent)
     : QListWidget(parent)