These platforms integrate a file preview in their native filechoosers

Before: After a rightclick -> "Modify Account" on an account in the
roster the preferences of the account are shown but the account is not
selected in the account list.
After: account will be selected in the account list too

Use GtkFileChooserDialog only when we need previews, default to
NativeFileChooser otherwise.

GtkFileChooserDialogs have a long list of issues, so lets only use it
if we gain something from it.

Flatpak should only run NativeFileChoosers because its sandboxed and
this is needed for security purposes. As a result of that, Flatpak Users
dont have image previews in the FileOpenDialogs

Refactor all FileChoosers for a more simple approach when we use them

Add a new SendFileDialog, so we dont have to put widgets into the FileChooser
which forces non-native Dialogs.

regression was introduced in e2383fd7

Using a FileChooserDialog for this is overkill, use FileChooserButton
in the future

This was nonfunctional for a long time and nobody complained

- Move code into ui file
- Use FileChooserButton instead of FileChooserDialog
- Make methods private
- Simplify code

We use now a Gtk.FileChooserButton for client certs

Fixes #9083

Dont save fingerprints to config and check certs with our own methods.
We should trust openssl to do all necessary checks.

Self signed certs can be added to cacert.pem and will not show up as
an error until the cert changes.

nbxmpp now saves all ssl errors and passes them, so now we loop over
all errors until all are confirmed or ignored by the user

Also cacerts are now saved in utf-8

Fixes #9106

As all Windows versions have a status icon and most Windows users expect this

Fixes #9031

Fixes #9065

set_urgent is deprecated in favor of set_priority

Fixes #9101

Fixes #9094

‎* rename the remove_plugin function to uninstall_plugin because it
deletes files on the disc and uninstall is the label of the button which
triggers this function
* added a new remove_plugin function, which deactivates the plugin (if
needed), removes it from the list of managed plugins and deletes the
contents of sys.modules

This lets us now import the app module without setting paths

Remove as much as possible startup code from GtkApplication to stay
more true to our goal to separate GUI from the rest of Gajim

- Move everything translation related from gajim.py to i18n.py

Pass args to logging method instead of string formatting

This allows us to import the app module without triggering
dependency detection

Also add is_installed() for checking if a dependency is installed and
disable_dependency() in case we dont want to use a dependency