New manager webapp for Tomcat

[rmaucher]

This is a new more modern manager/admin webapp for Tomcat. The webapp is currently located in modules/manager2. This includes a testsuite.

What it is:

• A modern reactive webapp designed and implemented using OpenCode (with various models backing it up). It is meant to be tool maintained.
• Scales down to phone layouts and meant to be used or partially packaged as an application later.
• The UI is subject to subsequent changes, just like apps often get a fresh look once in a while.
• A lot of the more complex backend code remains in the existing Manager servlet (webapp deployment and management) and StoreConfig (saving a configuration back to the server.xml storage).
• Bring back the functionality of the Tomcat Admin webapp from Tomcat 5.

What it is not:

• A replacement for the tool endpoints (JMX scripting and deployment) provided by the existing legacy manager webapp.
• A component that will be released independently and has to support N different Tomcat releases. (why: see Maven plugin)
• A binary release. As a module, it will be source packaged in any future Tomcat 12-M release, but will not ship as a binary or anything. This can eventually move to the main source tree and be backported. Or not.

Use ant to build, ant deploy to put it in the output/build/webapps of the main folder to be able to run it, and ant test to run the tests (which takes time, basically most of the tests use a different config, some test deployment, edit and save to server.xml, so it's hard to avoid it even if I wanted to).

Please keep PR review focused on essentials:

• If you do not like it and do not want to see it merged, please say so (preferably before it is merged :) ). I will not complain since this was basically an experiment.
• Significant bugs or issues that must be addressed before merging.
• There are a few changes to the Tomcat to make TLS configuration more flexible with add/remove of stuff. It is not strictly needed, so I can take it out.
• I can rename the webapp. I named it "manager2", which works for me because it seemed like Manager Webapp 2.0 and it cannot fully replace the original one either.
• Please don't review any single trivial defect, we can see about it after merging. The code will go through the usual review/fix cycles anyway.
• It is Ant based (not Maven), but the directory layout was Maven inspired. I can fix it if needed.