Adds Type field and makes Request and Response interface{}.  

Add OptMarshaler interface for doing JSON marshaling with options.

Fixed typo: follwing/following.

Adds replication engine and core in-repo addon

gRPC updated to 1.20.1 which fixes a couple of important bugs.

Updates protos as well.

Multierror is not nil unless you return ErrorOrNil, so this was causing
non-nil errors to be returned when not expected.

Also we need to ensure we only call handleWALRollback if a function
exists.

Fixed typo: appropiate/appropriate

* http timeout fields are configurable

* move return statement for server config tests outside of range loop

* adds documentation for configurable listener http_* values

* fixed some formatting for the docs markdown

This obviates the need for a sort/eliminate duplicates step, giving a performance boost in some key distributions with large datasets.

Add optional HA support for postgres backend if Postgres version >= 9.5.

Closes #6711

UI: Add Toolbar