Fix Dashboard Nav Bookmarks

Fix Dashboard Navigation Bookmarks

- Check if page exists before adding item
- Remove item from User Config if page no longer exists
- Switch `is_object()` to `isError()` as `Page::getByID()` always
  returns a Page object
Merge pull request #1284 from mkly/fix_dashboard_quick_nav

Fix Dashboard Nav Bookmarks
Revert `TextHelper::preventWidows()`

Revert `TextHelper::preventWidows()`

Local testing and PHP Multibyte String Functions support issues.
Merge pull request #1285 from mkly/revert_prevent_widows

Revert `TextHelper::preventWidows()`
Version Bump to 5.6.2

Version Bump to 5.6.2
Revert Starup Session move Below Startup Packages

Revert startup session move below startup packages as this breaks full
page caching in certain ways

- Move `statup/session.php` back above `startup/check_page_cache`
- Change `require_once` back to `require`
Merge pull request #1286 from mkly/revert_dispatcher_move_startup_session

Revert Starup Session move Below Startup Packages
Revert Install Session Start

Revert install session start

First revert did not completely remove addition and causes warning on
install

- Completely remove require startup/session.php
Merge pull request #1288 from mkly/revert_install_session_start

Revert Install Session Start
page forbidden tweak because area is wrong anyway
gettin ready for 5.6.2.1 awwwww JEAH
Fix BlockController::getUniqueIdentifier()

Fix `BlockController::getUniqueIdentifier()`

- Use `getBlockID()` no `getIdentifier()` as `getIdentifier()` will
  already append the BLOCK_ prefix resulting in BLOCK_BLOCK_
Fix Merge Comment in db.xml

Fix Merge Comment in db.xml file
Merge pull request #1290 from mkly/fix_merge_comment_in_file

Fix Merge Comment in db.xml