QmlJS checks: Add @enable-all-checks annotation.

It enables all checks, even those that we deem to annoying to be
enabled by default.

Also fix a bug where some disabled checks had the wrong severity.

Change-Id: Id434ad62dabafac979ee2304a85d368b9ea98fa4
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@nokia.com>

src/libs/qmljs/qmljsstaticanalysismessage.cpp

@@ -158,9 +158,9 @@ StaticAnalysisMessages::StaticAnalysisMessages()
            tr("== and != may perform type coercion, use === or !== to avoid"));
     newMsg(WarnConfusingExpressionStatement, Warning,
            tr("expression statements should be assignments, calls or delete expressions only"));
-    newMsg(HintDeclarationsShouldBeAtStartOfFunction, Error,
+    newMsg(HintDeclarationsShouldBeAtStartOfFunction, Hint,
            tr("var declarations should be at the start of a function"));
-    newMsg(HintOneStatementPerLine, Error,
+    newMsg(HintOneStatementPerLine, Hint,
            tr("only use one statement per line"));
     newMsg(ErrUnknownComponent, Error,
            tr("unknown component"));