qmljs: better defaults, more uniform handling of paths

Uniform handling of the different qml dialects.

Now paths for a given document prefer the project of that document.

For Qt the following sequence is used:
- Qt of the project of the document
- Qt of the active target
- Qt used to run creator

Currently all paths of the open projects are still merged, but that
can be changed.

Change-Id: Id302c13c893b66fbfe24e301602fe69de152eed4
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>

src/libs/qmljs/qmljsviewercontext.h

@@ -42,8 +42,10 @@ class QMLJS_EXPORT ViewerContext
 public:
     enum Flags {
         Complete,
+        AddAllPathsAndDefaultSelectors,
         AddAllPaths,
-        AddQtPath
+        AddDefaultPaths,
+        AddDefaultPathsAndSelectors
     };
 
     ViewerContext();
@@ -52,6 +54,7 @@ public:
                   Flags flags = AddAllPaths);
 
     bool languageIsCompatible(Language::Enum l) const;
+    void maybeAddPath(const QString &path);
 
     QStringList selectors;
     QStringList paths;