details: Remove the "Getting software details…" label

Only show a spinner while loading, and remove the text.

https://bugzilla.gnome.org/show_bug.cgi?id=724669
details: Fade in the loading spinner

Fade in the spinner during 1000 ms. Since most PK backends are now
sufficiently fast to load the package details in a fraction of second,
this avoids needlessly flickering the spinner.

https://bugzilla.gnome.org/show_bug.cgi?id=724669
details: Use application/x-executable icon for local packages

https://bugzilla.gnome.org/show_bug.cgi?id=724669
details: Add CSS for infobar theming

... as per latest mockups.

https://bugzilla.gnome.org/show_bug.cgi?id=724669
details: Show the filename for local package installation

https://bugzilla.gnome.org/show_bug.cgi?id=724669
details: Align package details as per latest mockups

This makes the details section wider and aligns the two columns of
information as per latest mockups. The width of the columns and the
headings is now controlled by two size groups.

https://bugzilla.gnome.org/show_bug.cgi?id=724669
details: Let the 'origin' span 3 columns

This can be a really long text and doesn't look good when ellipsized:
could be e.g. "Fedora - Rawhide - Developmental packages for the next
Fedora release" or a particularly long local package name.

https://bugzilla.gnome.org/show_bug.cgi?id=724669
details: Remove spacing between infobar labels

https://bugzilla.gnome.org/show_bug.cgi?id=724669
details: Don't show missing history on a local package install

https://bugzilla.gnome.org/show_bug.cgi?id=724669
details: Remove duplicate copy-pasted code

https://bugzilla.gnome.org/show_bug.cgi?id=724669
Support the AppStream <project_license> tag

This is renamed from the original confusing <licence> tag.