CorePlugin: Compile with QT_NO_CAST_FROM_ASCII.

- Wrap literals in QLatin1String()/QLatin1Char().
- Extract some string constants avoiding repeated
  QString construction.
- Fix repeated invocation of Container.end() in loops.

Change-Id: If737735507aaf82e53063adda53f54c46418f42f
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>

src/plugins/coreplugin/id.cpp

@@ -87,7 +87,7 @@ QString Id::toString() const
 
 Context::Context(const char *id, int offset)
 {
-    d.append(Id(QString(id) + QString::number(offset)).uniqueIdentifier());
+    d.append(Id(QLatin1String(id) + QString::number(offset)).uniqueIdentifier());
 }
 
 void Context::add(const char *id)