RFR: JDK-8290011: IGV: Remove dead code and cleanup [v11]

[Tobias Holenstein]

> Remove dead code from the IGV code base. There are many unused or redundant functions in the code

Tobias Holenstein has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 45 commits:

 - Merge remote-tracking branch 'origin/master' into JDK-8290011
 - Undo removal of toString() in Group.java
 - make fond constants uppercase
 - more code cleanup
 - style update 2
 - delete unused Graph.java and Edge.java
 - Code style update
 - remove unused MouseOverAction
 - access static front in Diagram without getter
 - Merge branch 'JDK-8290011' of github.com:tobiasholenstein/jdk into JDK-8290011
 - ... and 35 more: https://git.openjdk.org/jdk/compare/91a23d77...1a3f7d09

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Changes: https://git.openjdk.org/jdk/pull/10197/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10197&range=10
  Stats: 4819 lines in 120 files changed: 336 ins; 3893 del; 590 mod
  Patch: https://git.openjdk.org/jdk/pull/10197.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10197/head:pull/10197

PR: https://git.openjdk.org/jdk/pull/10197