File manager should always return a value when form is submitted

If you would clear a file from the file manager popup, it would not get saved. If you would reload the page and edit the block, the file would still be there. The reason for that is that the file manager would return no value when no file is present. I think it's better to change that, so you can add the file manager to a block and have the 'clear' functionality work out of the box.
Fix adding attribute keys and categories in packages.
PSR-2
Fix tight coupling in database manager
Merge pull request #1367 from infostreams/patch-7

File manager should always return a value when form is submitted
Tweaks to app.php
Fix #1377
Merge branch 'develop' of github.com:concrete5/concrete5-5.7.0 into develop
recasing service.php
block clear
Fixing javascript error when switching between sub-panels
Set correct base path.
adding install check for innodb database tables
Fix javascript error changing permissions on pages in the sitemap
Adding search button to marketplace search; fixing add-on sets not showing up properly in search; making filter by set work
Fix force upgrade not working.
Fix exclude page list not working

Fixes #1389
PSR2 for inspect controller; fixing Undefined class constant 'FILENAME_PAGE_TEMPLATE_DEFAULT_ICON'
renaming some page template files for better standards
Fixing random unavailable attribute key