RFR: 6687: Add icon to the flame view to render as icicle graph

[Miroslav Wengner]

ticket: https://bugs.openjdk.java.net/browse/JMC-6687

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Commits:
 - 63e61ed9: 6687: icicle, flame graphs group actions, messages, icons
 - 9ce1a118: Adding icicle versions of the icons
 - d7ca4ef5: Adding icons
 - 552ab684: 6687: init icicle graph

Changes: https://git.openjdk.java.net/jmc/pull/50/files
 Webrev: https://webrevs.openjdk.java.net/jmc/50/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JMC-6687
  Stats: 297 lines in 12 files changed: 277 ins; 2 del; 18 mod
  Patch: https://git.openjdk.java.net/jmc/pull/50.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/50/head:pull/50

PR: https://git.openjdk.java.net/jmc/pull/50