libreofficekit: add a way to invoke getCommandValues()
- add a new button to the toolbar to invoke the getCommandValues() LOK
API with user-provided command name (and parameters)
- log the result using g_info(), which is visible on the console if
gtktiledviewer is started with G_MESSAGES_DEBUG=all
- change some labels to tooltip texts that actually show up on mouse
hover so you can understand what button does what
- tweak the icons, so the question mark icon is the getter and the info
icon is the setter
Change-Id: If6984d2dde3d669b42aafcc3f58a0ca757ccaaff
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/143477
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins