Settings link in Plugins overview and Manage blocks

[ferishili]

This PR fixes #379,

Description

In Plugins overview and Manage blocks pages, there is a possiblity for plugins to offer a shortcut link to their settings page.
Currently most of opencast plugins does not offer this possiblity.

Solution

With changes in this PR the settings shortcut link is now offered but in specific ways:

And by clicking on settings link you will end up in seperate category which contains a link to main settings:

From there you can click on Opencast Videos Settings whihc redirect to the main settings.

Reason and explaination

The reason to do it this way is because of minimizing the changes and impacts that comes after that, because the plugin from start is using the wrong name for its setting category and changing it now requires to change a lot of things including tool_openacst plugin, so I have decided to provide a forwarding mechanism!

For block plugins in Moodle it is necessary to use the main amdin setting category with specific naming (see https://github.com/moodle/moodle/blob/ab5692acdf1f9a2b3cf06986f49b951558793f38/lib/classes/plugininfo/block.php#L103)
in format of 'blocksetting' . $this->name, which for block opencast it ends up with "blocksettingopencast".
The setting shortcut link only appears when a plugin has that category in its settings.

To TEST

• Patch this PR
• Navigate to Site admin > Plugins > Plugins overview.
• Locate the block_opencast
• Click on Settings shorcut link.
• You would endup in a new setting page, locate the Opencast Videos Setting link and click on it.
• You then will be redirected to main settings of block opencast plugin.

UPDATE

This PR depends on a very important bug fix in tool_opencast plugin: Opencast-Moodle/moodle-tool_opencast#74
Which will fix the issue of failing test ci steps!