Port to AyatanaAppindicator3

[kekePower]

Description

I am using Mageia Cauldron and it doesn't have AppIndicator3, but instead uses Ayatana.

Am running it now and it works as expected.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• [x ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x ] This change requires a documentation update

How Has This Been Tested?

Before doing this I had to "disable" the trayicon to get pulsemeeter running. Now I have the trayicon and the app working.

• Test A
• Test B

Checklist :

You don't need to do all of this, but at least check what you did

• [x ] My code follows the style guidelines of this project
• [x ] I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• [x ] My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• Any dependent changes have been merged and published in downstream modules