Fix display name of created shortcut after dropping from another application.

The display name is available on linking only if the linked file is already
retrieved (in the folder for example). Otherwise the basename is assumed.
The commit fixes that so display name is directly retrieved in the operation.
Correctly use parent window screen for context in fm_launch_command_simple().
Commit from LXDE Pootle server by user jleclanche.: 1150 of 1565 strings translated (345 need review).
Commit from LXDE Pootle server by user safaalfulaij.: 1856 of 1565 strings translated (24 need review).
Add KDE archiver "Ark" in archiver integration.
[SF#887]Use list returned by g_get_system_{config,data}_dirs() in right order.

The first value in such list is more relevant so next one should not overwrite it.
That was incorrectly handled in config loader and thumbnailers loader. Fixing it.
Add setsid() into child setup after g_spawn_async().

This way an application that was started will never die after our
application (i.e. parent) was closed.
Fix over previous commit: setpgid() should be used instead of setsid().

If we use setsid() then spawned process will daemonize and there is a chance
it will survive desktop session end. That should be made impossible.
Don't use $sysconfdir but XDG_CONFIG_DIRS should be used for config load.
Fix possible memory leak in fm_config_load_from_file().
Use g_content_type_guess() always with file name, not just with sample.

Some file types may be recognized incorrectly.
[SF#892]When calculate total file sizes in directory, skip filesize of directory.

Directory size is not much relevant as it cannot be "copied" as it is.
[SF#895]Use callback read_image_from_file instead of read_image_from_stream for thumbnails.

Since we need to check image size in Mpix to abort too big images to be loaded,
we cannot load file before calculating its size and we don't have any callback
to read its size beforehand. Therefore we have to read whole file there.
Update indentation in src/base/fm-thumbnail-loader.c.
[SF#895]Check image sizes and abort loading image if it's Mpx is above thumbnail_max.

This should be reflected in the Preferences on next strings change.
[SF#871]Use g_desktop_app_info_new_from_filename() not g_desktop_app_info_new().

The latter call somehow fails in newer GLib and returns NULL on fresh created
file, and that doesn't happen in test program.
Anyway, g_desktop_app_info_new_from_filename() is definitely faster.
ABI bump in preparation for release 1.2.2 (soname 4.0.1 -> 4.0.2).
NEWS file update.
Release 1.2.2.
Fix installation of libfm-extra.pc file for development with it.