With this Gajim loses the ability to draw animated GIFs in the Roster

GIFs have numerous drawbacks:

- We cant add them to the IconTheme, which means we need a different interface to load them
- The IconTheme scales all icons we load for the current scale (HiDPI)
- The animation causes many updates to the Roster, and causes high cpu usage

Fixes #8814, #8655

This is needed for tests to work

- Use parse_datetime()
- Improve tzo node validation

The added account causes an issue with test_gui_interface,
so the account needs to be removed again

- Move updating tags into HtmlTextView
- Rename some vars
- Remove legacy GTK code

Remove checking for font_scale, Gtk.TextIter.get_attributes() seems buggy at
the moment, and we dont need to check the current scale to apply a new scale

Fixes #9067

data is now a str

Otherwise we have to guess the encoding of the host system

This is a regression from e281fb68

Fixes #9440

Andrey Gursky authored 6 years ago and Philipp Hörist committed 6 years ago

Fixes #9427

Fixes #9438

When a relative custom config path is passed via commandline, the logic
which decides if a plugin can be deleted from the plugin manager fails

This reduces problems with old plugins without max version

This excludes other unix systems which was not intended

Its listed as dependency

sys.platform == 'linux' excludeds other unix systems, for example FreeBSD

Its a standard library which will be always available in our builds

Code is also not cross-platform compatible

- sys.platform == 'linux', excludes many other unix systems
- use shutil.which() to test if a command is available