Implement syntax highlighting in diff editor

All Qt Creator's main highlighters are used in the first place,
for other mimetypes generic highlighter is used as a fallback.

Task-number: QTCREATORBUG-9580

Change-Id: I863b9085520e5bdda142ce88f2074afeacee0531
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Petar Perisin <petar.perisin@gmail.com>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>

src/plugins/pythoneditor/pythoneditor.pro

@@ -18,6 +18,7 @@ HEADERS += \
     wizard/pythonclasswizarddialog.h \
     wizard/pythonsourcegenerator.h \
     tools/pythonhighlighter.h \
+    tools/pythonhighlighterfactory.h \
     tools/pythonindenter.h \
     tools/lexical/pythonformattoken.h \
     tools/lexical/pythonscanner.h \
@@ -34,5 +35,6 @@ SOURCES += \
     wizard/pythonclassnamepage.cpp \
     wizard/pythonsourcegenerator.cpp \
     tools/pythonhighlighter.cpp \
+    tools/pythonhighlighterfactory.cpp \
     tools/pythonindenter.cpp \
     tools/lexical/pythonscanner.cpp