[IMP] translate: unify the server and web translation export mechanisms

[IMP] translate: unify the server and web translation export mechanisms

- qweb and Javascript terms extraction now builtin
- all qweb/JS terms are flagged with an extra PO comment:
  `openerp-web`, which the web client will use when
  loading translations
- the homemade Python/Mako extractor has been removed
  and replaced by the default babel Python extractor.
  Net result is that we extract less spurious terms, but
  keep valid ones, so everything looks great under
  the sun.

bzr revid: odo@openerp.com-20121003132659-h5obyl1j7hjo1y2b