Fix #3030.

Previously, table configuration stored server references as names.
Now they are stored as UUIDs. The format presented to the user is
the same. But now, if the user renames a server, all of the table
configs will appear to "update" to reflect the new name, and if the
user declares a server dead, it will disappear from all of the
table configs.
Add back in guarantee that each shard's director is set exactly once.
Merge branch 'reql_admin' of github.com:rethinkdb/rethinkdb into reql_admin
adding admin issues table
using common functions for converting uuids and strings to datums
putting artificial reql tables back in alphabetical order
using different string for unknown or deleted items in issues
changing error string for writing to issues table
change to issue tracker home thread when reading rows
removing log_write_issue_tracker_t::entry_t interface
removing unnecessary templatization
changing description string for outdated index issues
making uuid_u::from_hash comply with RFC4122
moving templatized uuid_u::from_hash into issue_t
no longer include outdated indexes for deleted tables
removing unused metadata field
renaming name conflicts to name collisions
reorganizing issue tracking classes
removing unused files
breaking up issue_t::get_info_and_description into two functions