RFR: 7167: Agent Plugin

[Joshua Matsuoka]

This PR adds the Agent Plugin to JMC. This is a plugin for controlling the jmc agent and provides a way to attach it and add probes to any JVMs in the JVM browser, as well as providing a preset manager for creating/modifying probe presets.

There is still a small amount of cleanup to be done so I'll mark it as a draft for now but it would be great to get a review :)

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Commit messages:
 - Update with jmc-graphics icon for agent/agent plugn
 - Merge remote-tracking branch 'upstream/master' into agent-plugin
 - Updating copyright headers
 - Clean up spotbugs excludes
 - 7167: Agent Plugin

Changes: https://git.openjdk.java.net/jmc/pull/226/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=226&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7167
  Stats: 9049 lines in 73 files changed: 9049 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jmc/pull/226.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/226/head:pull/226

PR: https://git.openjdk.java.net/jmc/pull/226