[pLog-svn] Permissions in LT 1.2

[Oscar Renalias]

I have already finished integrating a finer-grained permission system
in the development version of 1.2, but only for the public side of the
blog (so that there can be users who can only post and update
articles, for example, as opposed to having access to also categories,
links, link categories, etc)

There was clearly a need for this permission framework so here it is.

For the admin side, I was thinking that being marked as an
administrator is more than enough. Do we really need "quasi-admin"
users who can change the site settings but cannot edit site users? Or
users who can create new blog categories but do nothing else?

I'd like to hear your feedback :)