Make a distinction between moderators and admins (#619)

* Make a distinction between moderators and admins

And rework the user list in the moderation interface, to be able to run the same action on many users,
and to have a huge list of actions whithout loosing space.

* Make user's role an enum + make it impossible for a moderator to escalate privileges

With the help of diesel-derive-enum (maybe it could be used in other places too?)

Also, moderators are still able to grant or revoke moderation rights to other people, but maybe only admins should be able to do it?

* Cargo fmt

* copy/pasting is bad

* Remove diesel-derive-enum and use an integer instead

It was not compatible with both Postgres and SQlite, because for one it generated a schema
with the "User_role" type, but for the other it was "Text"…

* Reset translations

* Use an enum to avoid magic numbers + fix the tests

* Reset translations

* Fix down.sql

migrations/sqlite/2019-06-21-154916_themes/down.sql

@@ -44,7 +44,6 @@ CREATE TABLE users_before_themes (
     display_name VARCHAR NOT NULL DEFAULT '',
     outbox_url VARCHAR NOT NULL UNIQUE,
     inbox_url VARCHAR NOT NULL UNIQUE,
-    is_admin BOOLEAN NOT NULL DEFAULT 'f',
     summary TEXT NOT NULL DEFAULT '',
     email TEXT,
     hashed_password TEXT,
@@ -59,6 +58,7 @@ CREATE TABLE users_before_themes (
     last_fetched_date TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
     fqn TEXT NOT NULL DEFAULT '',
     summary_html TEXT NOT NULL DEFAULT '',
+    role INTEGER NOT NULL DEFAULT 2,
     FOREIGN KEY (avatar_id) REFERENCES medias(id) ON DELETE SET NULL,
     CONSTRAINT blog_authors_unique UNIQUE (username, instance_id)
 );
@@ -68,7 +68,6 @@ INSERT INTO users_before_themes SELECT
     display_name,
     outbox_url,
     inbox_url,
-    is_admin,
     summary,
     email,
     hashed_password,
@@ -82,7 +81,8 @@ INSERT INTO users_before_themes SELECT
     avatar_id,
     last_fetched_date,
     fqn,
-    summary_html
+    summary_html,
+    role
 FROM users;
 DROP TABLE users;
 ALTER TABLE users_before_themes RENAME TO users;