[repoapi] introduce a basic ClientConnection class This is the new official way to access the repo from client side. It still access Session object directly as the server side connection is not up yet (and it's not up because it would have no user). Multiple follow up commit will install compatibility with the DBAPI. This will ease the migration from dbapi to repoapi. ClientConnection has no user yet but later commit will use it in the whole Web stack. related to #2503918

addressbook
basket
blog
book
calendar
comment
company
email
file
folder
i18ncontent
keyword
link
mailinglist
person
tag
timeseries
vcsfile