fix typo
[FIX] README: grammar
[FIX] CONTRIBUTING: dead link
[FIX] models: do not prefetch fields to recompute, and recompute once only

The method _prefetch_field() was accidentally prefetching fields to recompute;
which was skipping the actual recomputation, since a value was put in cache.
But sometimes the field's value was fixed by an extra recomputation of the
field.  Here we remove the extra recomputation and fix the cache corruption.
[IMP] models: do not use compute methods to determine default values anymore

Compute methods could give results that should not be considered as default
values.  For instance, a related field usually defaults to a null value, which
is then set to the field with its inverse method by create().  This may violate
a non-null constraint if the original field is required.  Therefore, compute
methods are no longer used to determine default values.
[FIX] models: on update, call inverse function on field even when it is stored

The inverse function of a stored computed field was not called when creating or
writing on a record with such a field.
[FIX] website_blog: Fixed the next post loop issue.
[FIX] website_blog: ordered by visits(desc) to display most visited blogs first.
[FIX] website_blog: Check if the blog post visited earlier by client are unpublished/deleted or not, and if yes then such posts need to be skipped when blog posts are being reaccessed using cookies('visited_blogs').