Link to templates plugin is broken

[Documentation on the templates](https://badoo.github.io/MVICore/extras/templategeneratorplugin/)

Proposes to download `MVICoreFileTemplates.jar` from https://github.com/badoo/MVICore/blob/master/plugin/MVICoreFileTemplates.jar?raw=true.

I can see that templates plugin can be found here:
https://github.com/badoo/MVICore/blob/master/plugins/MVICoreFileTemplates.jar

We need to update link

Open the templates documentation at extras/templategeneratorplugin/ and inspect the download link for MVICoreFileTemplates.jar. Update it to point to the plugin location under plugins/, then verify that the published documentation link resolves to the template JAR.

Written by the indexing model from the issue text.