RFR: 7041: Add Percentage column based on Duration in stack trace view

[Suchita Chaturvedi]

This PR address the enhancement requested by one of our customers where they were missing the percentage column by duration in stacktrace view which was available in JMC 5.5. Currently we have percentage column which is calculating the percentage based on event count and there is no way user can configure that.

Since this functionality might not be used by many customers I have added a toggle icon in Stacktrace View so that user can set the view according to his preference and by default the new column will be hidden.

Default view showing toggle icon:
![image](https://user-images.githubusercontent.com/11155712/120366242-1056ca00-c32d-11eb-8c27-ac7481fc89cf.png)

Percentage By Duration Column :
![image](https://user-images.githubusercontent.com/11155712/120366404-3ed4a500-c32d-11eb-82b7-6107d790fdca.png)

Please review the change and let me know your valuable feedback on this.

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Commit messages:
 - 7041: Add Percentage column based on Duration in stack trace view

Changes: https://git.openjdk.java.net/jmc/pull/257/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=257&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7041
  Stats: 145 lines in 4 files changed: 140 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jmc/pull/257.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/257/head:pull/257

PR: https://git.openjdk.java.net/jmc/pull/257