Add Cinnamon support for notification actions and improve support for more types of email clients (e.g.: web apps)

[victor-marino]

Hi!

This very simple PR improves support for notification actions when an email is received, as partially reported in #5. It only affects the libnotifyplugin.py file.

1. Add Cinnamon as a supported desktop environment for notification actions

Right now, the notifications plugin is hard-coded to only enable notification actions if the _is_gnome_environment() function detects Gnome as the current desktop environment.

Given the actions are equally supported in Cinnamon, I've simply added the cinnamon string to the values that return true, and renamed the relevant functions to reflect this. E.g.: _is_gnome_environment() -> _is_supported_environment().

Also extracted the supported environments as a list at the beginning of the file for easier readability and expandability if ever needed.

2. Launch email client properly by using Gio.AppInfo.launch() instead of start_subprocess()

For some reason, the current code is fetching the name of the executable that launches the email client with Gio.AppInfo.get_executable(app_info), then trying to launch that executable through the low level function start_subprocess(mailclient). Not only is this completely unnecessary, but is also a very fragile implementation and breaks compatibility with any email client that isn't a native app.

For instance, I'm using a Fastmail web app as my default email client (Mint's built-in web apps feature is awesome). This means the launch command associated with it is:

sh -c 'XAPP_FORCE_GTKWINDOW_ICON="web-fastmail" firefox --class WebApp-Fastmail3699 --name WebApp-Fastmail3699 --profile /home/MyUser/.local/share/ice/firefox/Fastmail3699 "https://betaapp.fastmail.com"'

With the current implementation, the "executable" that is fetched by the plugin is sh, which obviously means nothing happens when I click the notification.

By changing the code to use the more robust Gio.AppInfo.launch(AppInfo) function directly, the email client is launched correctly regardless of the app type. And as a bonus, we get to delete some code and remove an import 😬

I think it should be fairly straightforward to merge, but let me know if I should make any changes!

[victor-marino]

@tikank just pinging you about this.

Did you get a chance to take a look at the PR?