add missing fields in REST API devices doc
add options parameter to device REST API
update switchboard configuration
update developers documentation around provisioning plugins
remove reference to Aastra 6751i

The only plugin supporting it was the xivo-aastra-2.6 plugin, which has
been removed earlier this year.
move detailed upgrade notes into their own directories
upgrade notes for switchboard phone configuration
add archive provisioning plugins repository
add note about old switchboard plugins
Merge branch '5002-switchboard-opt'