[FEATURE] Add context-menu for template-icon in the "Template"-view

Allows to easily copy, delete, (de)activate etc. the template.

Resolves: #46058
Releases: 6.1
Change-Id: I2dfc96da13fdec9807a05ef3764d40db76aa1c4e
Reviewed-on: https://review.typo3.org/18846
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn