go: re-do the entire thing

This is a mega-change, but attempting to split this up further is
probably not worth the effort.

Summary:

1. Bump up bazel, rules_go, and others.
2. Switch to new go target naming (bye bye go_default_library)
3. Move go deps to go.mod/go.sum, use make gazelle generate from that
4. Bump up Python deps a bit

And also whatever was required to actually get things to work - loads of
small useless changes.

Tested to work on NixOS and Ubuntu 20.04:

   $ bazel build //...
   $ bazel test //...

Change-Id: I8364bdaa1406b9ae4d0385a6b607f3e7989f98a9
Reviewed-on: https://gerrit.hackerspace.pl/c/hscloud/+/1583
Reviewed-by: q3k <q3k@hackerspace.pl>
diff --git a/.bazelrc b/.bazelrc
index dc92a13..9d3a556 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -6,3 +6,5 @@
 build --workspace_status_command=./bzl/workspace-status.sh
 test --build_tests_only
 test --test_output=errors
+build --cxxopt=-std=c++14
+build --host_cxxopt=-std=c++14