logic: Added PCH support to CDB source groups (issue #311)

* added PCH Flags list and checkbox to reuse compiler flags and cdb flags to source group setup
* added UI tests for C++ and CDB source groups

testing/project_setup/cxx_cdb_pch/checklist.txt

@@ -0,0 +1,26 @@
+* Run "1_setup.sh"
+* Start up Sourcetrail
+* Click "New Project"
+* Enter a project name
+* Set "./working_copy" as project location
+* Click "Add Source Group"
+* Select "C++" -> C/C++ from Compilation Database"
+* Click "Next"
+* Pick "compile_commands.json" at "Compilation Database"
+* Click "show source files" button
+* Validate "Source Files" list contains "src/main.cpp"
+* Click "OK"
+* Validate "Header Files & Directories to Index" contains "src" entry
+* Add "**/Foo.h" to "Excluded Files & Directories"
+* Click "Next"
+* Click "Next"
+* Add "-DCOMPILER_FLAG" to "Additional Compiler Flags"
+* Add "./src/pch.h" to "Precompiled Header File"
+* Add "-DPCH_FLAG" to "Precompiled Header Flags"
+* Click "Create"
+* Validate "All files" is the only option selectable
+* Click "Start"
+* Validate Project indexed without error
+* Click "OK"
+* Close Sourcetrail
+* Run "2_teardown.sh"