Organised activity types and moved most to repos

Repos are generally better since otherwise we end up duplicating
things between front-end and API.

Types moved to by CONST values within a class for better visibilty
of usage and listing of types.

app/Actions/ActivityType.php

@@ -0,0 +1,22 @@
+<?php namespace BookStack\Actions;
+
+class ActivityType
+{
+    const PAGE_CREATE = 'page_create';
+    const PAGE_UPDATE = 'page_update';
+    const PAGE_DELETE = 'page_delete';
+    const PAGE_RESTORE = 'page_restore';
+    const PAGE_MOVE = 'page_move';
+    const COMMENTED_ON = 'commented_on';
+    const CHAPTER_CREATE = 'chapter_create';
+    const CHAPTER_UPDATE = 'chapter_update';
+    const CHAPTER_DELETE = 'chapter_delete';
+    const CHAPTER_MOVE = 'chapter_move';
+    const BOOK_CREATE = 'book_create';
+    const BOOK_UPDATE = 'book_update';
+    const BOOK_DELETE = 'book_delete';
+    const BOOK_SORT = 'book_sort';
+    const BOOKSHELF_CREATE = 'bookshelf_create';
+    const BOOKSHELF_UPDATE = 'bookshelf_update';
+    const BOOKSHELF_DELETE = 'bookshelf_delete';
+}