Add support for scanning javascript files.

Add support for scanning javascript files.

Javascript may contain ".import" pragmas/statements,
which should be treated in a similar way as qml file
imports.

Add findQmlImportsInJavascriptFile() which extracts and
parses the .import lines. Refactor findQmlImportsInFile()
to handle both .qml and .js and call out to the correct
parsing function.

Add "-jsFiles" for specifying javascript
files on the command line similar to "-qmlFiles".

Task-number: QTBUG-35349

Change-Id: I6b8e0cc254c1edcf16940bec5cfda7c2637f115e
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>