This PR moves Filters from left sidebar to Search Tools.

Testing instructions

You have to install some old extensions for which newer versions are available. Make sure that you install extensions with different Type / Folder / Client so that you can test the various settings of the Filters.

For my tests with Update I chose the following extensions because I use them often and I had some old versions available:
Name | Type | Version | Folder | Client
Akeeba Backup | Component | 4.0.5 | N/A | Administrator
DJ-ImageSlider Package | Package | 2.2.4 | N/A | Site
JCE Editor | Component | 2.4.3 | N/A | Administrator
JCE MediaBox (J2.5 - 3) | Plugin | 1.1.17 | system | Site

For my test with Discover I copied the templateDetails.xml of an admin and a site template,
and the .xml manifest file of an authentication Plugin,
and changed those to get some fake extensions that Joomla could discover to install.

Before this PR

Extensions > Manage > Update

1. Left sidebar has 3 filter options (Select: Location, Type, Folder) that cannot be reset easily to original state with one button.

Extensions > Manage > Discover

1. Left sidebar has 3 filter options (Select: Location, Type, Folder) that cannot be reset easily to original state with one button.

Extensions > Manage > Discover & clicked on [Discover] button

1. Left sidebar has 3 filter options (Select: Location, Type, Folder) that cannot be reset easily to original state with one button.

After this PR

Extensions > Manage > Update

1. The Filters have been moved from sidebar to Search Tools in middle column. All filters can be reset with the "Clear" button. Note: the Filters work okay because the lists are filtered on basis of those filters. However the filters do not keep their chosen value. I hope that someone else understands the problem and can fix that.

Extensions > Manage > Discover

1. The Filters have been moved from sidebar to Search Tools in middle column. All filters can be reset with the "Clear" button.

Extensions > Manage > Discover & Search Tools + Select Type Option has been clicked

1. The Filters have been moved from sidebar to Search Tools in middle column. All filters can be reset with the "Clear" button. Note: these Filters work okay and they keep their chosen value.