Renderer: Increased particle texture maximum from 32 to 300

Defined additional 'pt_tex' flags for the new enum values.
Client|UI: Added ProgressWidget

Work in progress... (pun not intended)
Client|UI|ProgressWidget|Default Style: Basic implementation done

The ProgressWidget geometry is generated based on the old busyvisual
code.

The Default Style now contains colors for the progress widget, and
the wheel/gear images were copied into the pack.

LabelWidget can now be given a custom color that is multiplied into
the label image.
Client|Default Style: Added the border glow definitions and image
Client|Widgets: Drawing border glow as part of GuiWidget background

The border glow is applied in PopupWidget and ConsoleCommandWidget.
libgui|VertexBuilder: Making a 2D ring or circle
Client|Default Style: Adjusted border glow/shadow strength
Client|UI|Console: Don't show autocompletion popup if only one suggestion

There is little point in showing the popup if the only completion has
already been appended to the command line.
Fixed|LabelWidget|Client|UI: Image/text positioning, gap rule

LabelWidget now uses a style rule to define the gap between an image
and a text in the label. Also, image fitting was improved so that
it doesn't mess up text positioning: image is fitted completely
before the text is positioned beside it.
Client|UI|ProgressWidget: Drawing shadow behind wheel, improved layout with text

The ProgressWidget can now place a status text beside the wheel.
The layout of the drawn wheel matches the old one in busyvisual.
Also, a shadow is drawn behind the wheel using
VertexBuilder::makeRing.

Todo: Cleanup, visual tweaks.
Merge branch 'master' into shadow-bias-c++