Clang: Use the tree instead of the list for Clang-Tidy settings

List of checks does not give enough flexibility to
select/unselect specific checks. The tree fixes that.

Also remove Clang-Tidy checks line edit because it is
now integrated into the tree mode as an alternative way
of providing checks by pressing "Plain text edit" button.

'cpptools_clangtidychecks.h' is generated using python
script 'generateClangTidyChecks.py' and clang-tidy
from our LLVM/Clang 6.0 build.

Change-Id: I2ed1738cb2cbbf8dac6aba563469f06f69b11593
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

src/plugins/cpptools/cpptools.pro

@@ -100,7 +100,8 @@ HEADERS += \
     cppsymbolinfo.h \
     cursorineditor.h \
     wrappablelineedit.h \
-    usages.h
+    usages.h \
+    cpptools_clangtidychecks.h
 
 SOURCES += \
     abstracteditorsupport.cpp \