merge mate-indicator-applet and sensors-applet into mate-applets

[mbkma]

If this gets merged, https://github.com/mate-desktop/mate-indicator-applet and https://github.com/mate-desktop/mate-sensors-applet can be archived

[lukefromdc]

I just got a clean build and install of this on Debian and running in wayland. For some reason the indicator applet silently failed to render, with no text showing up when running the panel from terminal with
mate-panel --replace
This however is not new, I've rarely been able to get it to run properly in Debian. Neither removing the tray applet nor disabling the panel's native SNI support nor restarting an indicator got it to show up. If it's just not connecting it should read "no indicators."

No issues at all with the sensors applet.

Distros in which the indicator applet is known not to work probably should disable it at built-time or simply not ship it in their packages. Note that if they desire, distros such as Debian-based distros that split up binary packages from one source package need not change anything in their distributed packages except the name of the source package. Any one source package->one binary package distros will of course have to mark mate-applets as replacing the merged-in packages. This is at least how I manage my local builds

[lukefromdc]

Note that this will simplify any future mate-wide/all repo fixes by eliminating two packages.

[lukefromdc]

Do we want to do this within 1.28 (possibly throwing a curve at distros) or bump version to 1.29 knowing we will have to deal with the old repos until 1.30 comes out?

A third option does exist: bump version, merge this, bump version again to 1.30 and generally release 1.30 now. We'd have to fix translation issues breaking builds in some distros (which I do not know how to do) to do this of course. For now I do not update translations in any repo where this breaks builds, but 1.30 should not be released without fixing this and with this or two applets risk going English-only. That would be seriously ugly at any time but especially now given current events.

[mbkma]

I would go for 1.29. Not rushing anything. We should release 1.30 only if everything else is also stable and tested and then release all 1.30 packages at once.

[vkareh]

Merging the indicator applet into the overall mate-applets repo will be problematic for some distros. Fedora, for example, does not have the ayatana indicator service in the repo, and so the build will fail automatically (even if some of the ayatana libraries are included).

I think Ayatana is only used in Ubuntu, but may be wrong...