Cleanup
libgui|Image: Creating an Image with a solid color
Fixed|libgui|Atlas|AtlasTexture: Using atlas without a backing store

The first commit will define the size of the texture with undefined
contents, as there is no backing store where to get the rest of the
data.
Client|LineEditWidget: Cleanup
Fixed|libgui|Font: Adjusted text rasterizer to avoid clipping
Client|Widgets: Working on LogWidget

This is incomplete work presently, however the basic building blocks
are in place: log entries are received via a sink, they are wrapped
to multiple lines, and are then composed for GL drawing using
GLTextComposer. The entries near the visible range are kept ready for
rendering on a separate atlas.

Todo: Fix eventual corruption / overdraw / atlas misbehavior
Todo: Text styling (handle styling escape symbols in Font)
Todo: Performance -- too many calls to measure text's visible widths
Todo: Cleanup of LogWidget implementation