[IMP] fields: split the default value from the compute function

This separation allows to set a default value on a related field, for instance.
[FIX] event: jump on the correct menu after installing
the event application (event kanban view).

Also added a missing description on event.type model.
[FIX] doc: branch name in configuration

The branch name is used in the version switcher, so the master branch should have a version of "master".

Maybe the release could be the revision hash? Not sure how to extract it from the repo.
[FIX] website_sale: checkout: do not reset address country every time

Once the value is set it can be modified by the user
(e.g. if geoip detection was wrong), so should not be reset.
[REVERT] typo
[FIX] Adding __init__.py that addons are detected via root and might be imported without using the virtual openerp.addons path
[IMP/REF] Enabling inheritance of product.pricelist.items via context and additional methods without the need to overwrite method _price_get_multi() completely by adding two hooks