[IMP] Cache bundles in ir.attachments instead of a LRU

Forward ported from 8.0's commit: 8402625
[FIX] mail: bad test
[IMP] hr: strenghtening of write()
[FIX] bundles: fix compiled css assets recomposition

- Do not include css in less source because malformed css will break
  less compilation
- Always recompose compiled css, even if not in debug mode
- Less and sass compilers mode @at-rules on top in order to comply
  to css 2.1, those @at-rules where left-over during the recompostion
  because they lost their marker. Those are now handled as virtual
  inline stylesheets.
[FIX] ir.attachments of compiled css assets not properly invalidated
Update __openerp__.py

Little mistake in the descreption seen during translation.
Merge pull request #1875 from ma78nee/patch-1

Little description mistake
[IMP]Export Wizard: Added Button to Sort fields in Fields_to_export column