[PATCH] GUI's right panel types can clash

[Deiz]

While the display of construction and training icons in the GUI seems to be mutually exclusive, trading icons can be shown over top of other icons, e.g. if your first selected entity is a trader and your selection also includes a builder.

The patch also fixes a few related usability issues: Technologies are now listed provided there's only one row of icons, and the first selected unit's right panel is never clobbered by subsequent units.

An example of the latter occurs when selecting one of the few units that produces other units, followed by a builder (resulting in the trainable units disappearing).

[ben]

In 12123:

Fixes possible conflicts in unit command panel when selecting multiple entities, patch by Deiz/F00. Fixes #1524