jsbeautifier: move import

[Titotix]

When jsbeautifier.unpacker failed to import, exception is catch by JSAnalysis module and handled transparently.

To reproduce the error :
- You are in peepdf repo
- Create reproduct_error.py at ../ with :

 from peepdf import *
 from peepdf.PDFCore import *

 pdfparser = PDFParser()
 ret, pdf = pdfparser.parse(<pdf_file_toanalyse>)
 print pdf.getJavascriptCode(None)

Expected output : a list of java script code (obviously, if your pdf contains some)
Actual output : Error: An error has occurred while parsing an indirect object!!
And with forceMode=True, output will be an empty array.

With this patch, the same script will raise ImportException. This is a lot easier to understand and debug.