Update deps, general cleanup, improve roles UI, add role visibility.

[jnms-me]

Fixes #388

TODO:

• Add one final migration to convert roles.client_id into visibility:
  • NULL => global
  • NOT NULL => limited, add (role_id, client_id) to roles_limited_to_clients
• Use replace usages of role.client_id with visibility.

906cc56 tools(guix): Add manifest.scm.
f58a04a deps: Run cargo update.
7fe6750 deps: Run cargo upgrade.
869c225 deps(cargo): Update askama to 0.15.6.
948b35a deps(cargo): Complete the migration to askama 0.15.
4439844 lint: Fix rustc warnings.
c6edf03 style: Run cargo fmt.
3d7bbe8 feat: Add client column to the roles overview page.
a3a09a0 lint: Use $crate in macros.
845befb style: Organize imports.
d18bad8 build: Make package.json a private module.
2a3c9c7 style(templates): Use uniform spacing for inline rust code.
6833f07 style(editorconfig): Set html tab width to 2.
0c5959e style(editorconfig): Set charset and whitespace control flags.
a70709c lint(templates): Reformat and clean up html templates.
484223b refactor(templates): Replace match with if-let for Result types.
bb933e1 fix(ui): Correct typos in role page.
d6a7261 style(templates/roles): Use multilines for long input tags.
fa346ec feat(frontend): Add editable description to the show_role page.
ec60bc5 fix: Set content-type to html for error pages.
db7e67b tools(hooks): Remove preamble intended for pre-push from pre-commit.
d49d6fc feat(backend): Implement role_controller::update_description route.
10f882c tools(hooks): Add optional cargo sort-derives to pre-commit hook.
5803611 style: Sort derives.
c31c7f7 style: Use consistent order for route function args and add comments indicating source of the args.
c171c57 style: Order routes in lib.rs in their function declaration order.
0f3fadc chore(gitignore): Add .diesel_lock.
03e20d3 fix(migrations): Fix diesel schema.rs auto-generation, update docs.
5197621 db: Rename users_roles to users_assigned_roles and clients_roles to clients_assigned_roles.
c12049e db: Add visibility field to roles;
479861f db: Add roles_limited_to_clients table.
24bbbb6 feat(frontend): Add editable visibility to the show_role page.
398b34e feat(frontend): Use drop-downs for client/user selection on the show_role page.
0dcd557 feat(backend): Implement role_controller::update_visibility route.
46e9f57 style: Move roles_controller::delete_role to bottom of source file.
37d3580 feat(frontend): Improve error/success messages returned by roles_controller.
e2a8689 feat(backend): Implement roles_controller::add_limited_to_client route.
1453aa8 feat(backend): Implement roles_controller::delete_limited_to_client route.
a2e51ad feat(frontend): List “limited to” clients on show_role page.
316adda refactor(frontend): Use for-else for placeholders on show_role page.