Updated activities table format

Renamed some columns to be more generic and applicable.
Removed now redundant book_id column.
Allowed nullable entity morph columns for non-entity activity.

Ran tests and made required changes.

database/migrations/2020_11_07_232321_simplify_activities_table.php

@@ -0,0 +1,58 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Support\Facades\DB;
+
+class SimplifyActivitiesTable extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        Schema::table('activities', function (Blueprint $table) {
+            $table->renameColumn('key', 'type');
+            $table->renameColumn('extra', 'detail');
+            $table->dropColumn('book_id');
+            $table->integer('entity_id')->nullable()->change();
+            $table->string('entity_type', 191)->nullable()->change();
+        });
+
+        DB::table('activities')
+            ->where('entity_id', '=', 0)
+            ->update([
+                'entity_id' => null,
+                'entity_type' => null,
+            ]);
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        DB::table('activities')
+            ->whereNull('entity_id')
+            ->update([
+                'entity_id' => 0,
+                'entity_type' => '',
+            ]);
+
+        Schema::table('activities', function (Blueprint $table) {
+            $table->renameColumn('type', 'key');
+            $table->renameColumn('detail', 'extra');
+            $table->integer('book_id');
+
+            $table->integer('entity_id')->change();
+            $table->string('entity_type', 191)->change();
+
+            $table->index('book_id');
+        });
+    }
+}