Refactor CMake build scripts

1. Use FeatureSummary module to show configuration results.

2. Invert option()/find_package() relationship: instead of
calling find_package(... REQUIRED) when option is set, rely on optional
find package call and PackageName_FOUND variable.

3. Refactor handling options that result in simple preprocessor defines
(actually copy the snippet from libtorrent) so that everything is done
in a single function call.

4. Populate target properties in order to get rid of
include_directories() calls.

src/gui/properties/CMakeLists.txt

@@ -1,16 +1,7 @@
-include_directories(
-${CMAKE_CURRENT_BINARY_DIR}
-${CMAKE_CURRENT_SOURCE_DIR}
-../lineedit/src/
-)
-
-set(QBT_PROPERTIES_FORMS
+add_library(qbt_properties STATIC
 propertieswidget.ui
 trackersadditiondlg.ui
 peersadditiondlg.ui
-)
-
-set(QBT_PROPERTIES_HEADERS
 propertieswidget.h
 peerlistwidget.h
 proplistdelegate.h
@@ -25,9 +16,6 @@ pieceavailabilitybar.h
 proptabbar.h
 speedwidget.h
 speedplotview.h
-)
-
-set(QBT_PROPERTIES_SOURCES
 propertieswidget.cpp
 proplistdelegate.cpp
 peerlistwidget.cpp
@@ -42,6 +30,16 @@ speedwidget.cpp
 speedplotview.cpp
 )
 
-add_library(qbt_properties STATIC ${QBT_PROPERTIES_HEADERS} ${QBT_PROPERTIES_SOURCES} ${QBT_PROPERTIES_FORMS})
-target_link_libraries(qbt_properties qbt_base)
-target_link_libraries(qbt_properties Qt5::Widgets)
+target_link_libraries(qbt_properties
+    PRIVATE
+        qbt_gui_headers
+    PUBLIC
+        qbt_base qbt_lineedit Qt5::Widgets
+)
+
+target_include_directories(qbt_properties
+    PRIVATE
+        ${CMAKE_CURRENT_BINARY_DIR}
+    PUBLIC
+        ${CMAKE_CURRENT_SOURCE_DIR}
+)