[FIX] project: access task without project

Allow access to task without a project defined if the user is follower.
Fixes #3450
[FIX] product: pricelist shouldn't convert uom when not needed or incompatible uom types

Otherwise the Search More view will crash for example for sale order line because it will fetch the price of all products and then try to convert uoms for pricelist rule application without checking uom compatibility
[IMP] doc-ws: prepend setup code when copying from a snippet
[FIX] product: name_get of product.attribute.value

name was confusing for bom and product if the value of the attribute is display without the attribute name
added key in context to keep the previous behaviour (e.g. in product view where the attribute name is present)
[FIX] mrp: The attribute on bom lines is not filtered in function of the selected product template
[FIX] mail: _fields['type'].selection is a callable

This revert partially the rev. f2e4a10e1a58c932f9a989e642771f5ae75d756a

  File "/home/odoo/src/odoo/8.0/addons/mail/mail_mail.py", line 76, in default_get
      if context and context.get('default_type') and context.get('default_type') not in self._fields['type'].selection:
      TypeError: argument of type 'function' is not iterable
[ADD] ZeroClipboard-based "copy" button on snippets

Also fix ruby setup code, some of its bits were actually Python and didn't
quite work when pasted into irb...
[FIX] allow word wrapping in stripe-style code examples
[FIX] kanban view background is correctly set (web_kanban)

the .oe_background_grey class only changed part of the kanban background
when it was scrolled.  This makes sure that the full table has a grey
background.
[REF] account_anglo_saxon: refactor anglo saxon move lines

So that we can customise the real-time stock journal items made during sale invoice postings for certain companies who account for it slightly differently.
[ADD] doc: guide to the new API

Raw API documentation is not sufficient for people to learn the working
principles of the API, especially when they already know the old one. And some
things have changed since the opendays so the presentations don't reflect the
current state of affairs.

Closes #3483
[FIX] account: recompute date_due

Add on_change to recompute the due date when the invoice date is modified (it was only done when modified the partner_id field
Fixes #3413