Use YQUI icon loader in YQImage whenever possible

[shundhammer]

Trello

https://trello.com/c/5fgf38AA/

Bugzilla

https://bugzilla.suse.com/show_bug.cgi?id=1119688
https://bugzilla.suse.com/show_bug.cgi?id=1122174

Problem

Header icons for all the views of the partitioner were gone after the migration to theme icons and SVGs.

Cause and Fix

The YQImage had used an inconsistent approach to load the icons: If they could not be found in the desktop's theme, it would prepend :/ and append .svg to try to load them from the compiled-in Qt resource files, resulting in a path :/myicon.svg.

But that was wrong: It should have been either :/myicon or :/icons/myicon.svg. All icons in that compiled-in resource file are in a subdirectory icons/ with the .svg suffix, and there are aliases in the icon description file for just the plain name (without the .svg suffix).

Worse, it was a lot of code duplication; the reference how to do that is now the new YQUI::loadIcon() method. This is now used unless the image is specified with an absolute path (i.e. starting (!) with a / slash; but not :/).

This results in less code and more robust code.

Screenshots

(Notice the icons at the page headers)

[ancorgs]

Does this fix also applies to these other missing icons in the "configure" button? http://paste.opensuse.org/view//97095243

[shundhammer]

Does this fix also applies to these other missing icons in the "configure" button? http://paste.opensuse.org/view//97095243

Pretty sure no. This is only for the YQImage widget. That other thing is a menu button.

But the problem might be the same there, and the fix should be even easier: Just use YQUI::loadIcon() consistently and not let that widget do its own thing.

I just checked: it does use YQUI::loadIcon(). So maybe the icon names are just wrong (using a suffix or a path?).

[lslezak]

LGTM

I do not know what's wrong with Travis, I can build the package locally, but build in Docker for some strange reason fails. You can merge it even with failing Travis.