Use texvcjs for TeX sanitization

- return 'sanetex' attribute with the sanitized tex source
- detabify
- if the input can not be sanitized an error is returned
- note: mathoid uses the original user input for the actual
  processing and not sanetex

Change-Id: I20a4431a1277bb2c7a7a8bfadc5a7ef803f7e2ab