notification enhancements: icons, etc

[Antoine Martin]

See ​desktop notification specification.

The icons could be png encoded.
The actions would require us to check that the client supports the feature before we expose the server-side capability.

[Antoine Martin]

See #1688, #1375

[Antoine Martin]

new spec link (had gone 404)

[Antoine Martin]

Important bug fix in r17933: send icon data not path (which is often at best meaningless for a remote client).
Minimal backport in r17934.

[Antoine Martin]

More related changes:

• r17935: html5 client support
• r17936: fix usage via "xpra control"
• r17938 + r17940 + r17941: make win32 code reusable, win32 support (with py3k fix)

To test:

notify-send 'Hello world!' 'This is an example notification.' \
    --icon=/usr/share/xpra/icons/xpra.png

Already tested with:

• gnome shell, with both the python2 and the python3 client
• html5 client
• macos python2 and python3 clients (see also #1305 for why we don't use the native ones), python3 client porting work recorded here: ticket:1717#comment:4
• win32: python2 and python3

Note: some specific desktop environment may decide to block or hide the notifications..

Moving support for notification actions to #1735.

[Antoine Martin]

@maxmylyn: mostly a FYI, see comment:5.

[J. Max Mena]

Noted and closing.

[Antoine Martin]

r17973 (+r17974): the macos python3 client can now use the gtk notifier

(edit ticket title since "actions" have been moved to #1735)

[Antoine Martin]

r18195: when we need to show actions or when we don't have a native tray to bind to, fallback to using the gtk notifier.

This helps with #1688