Remove File Manager applet

[edalex-ian]

Is your feature request related to a problem? Please describe.

With the New UI work in 2021.1 it has been decided that we are definitely no longer supporting Internet Explorer (IE). As a result, there is no longer any purpose keeping the File Manager applet source in the project as the only browser which you can still run this in is IE.

Describe the solution you'd like

To remove the File Manager applet plugin source code (Source/Plugins/Applet/com.tle.web.filemanager.applet) and the integration with it. This includes things such as the JAR (Source/Plugins/Core/com.equella.core/jarsrc) but then also the integration points in the legacy UI.

Describe alternatives you've considered

There's been discussion about writing a modern day replacement with React. But at this point there doesn't seem to be high demand or support for that effort. If that changes, we can do so in the future.

Additional context

Also see:

• Deprecation notice in 2021.1; and
• Remove File Manager and In Place Editor applets #360
• Remove In Place Editor applet #2915