The current behavior of GetBlockList in the RemoteFortressReader
Protobuf RPC API is to only return blocks that have changed since
the last fetch. This causes problems when the RPC client (i.e. a
world renderer) wants to restart, as it can no longer fetch the
full world state.
This patch adds a `force_reload` option to BlockRequest, defaulting
to `false` (the current behavior). When passed, it returns all
requested blocks regardless of whether they have changed or not.
Signed-off-by: David Li <jiawei.davidli@gmail.com>