Changes

TileGrid: invalidateLayout not always called anymore on tile insertion

This happens since 4040e057cd2e04ef235b988fa06378b2fc9888ee.
 (commit: 8c45d06)

SplitBox: focus border of fields inside the split box not visible

The split box may contain a focusable field that uses a
focus glow (#scout.focus-border()), e.g. TreeField, Button etc.
Because split box sets overflow: hidden, the glow won't be fully
visible. Overflow: hidden is necessary if the content has a min size
and won't shrink anymore even if the splitter is moved further.

With the new overflow: clip property it is possible to define a
clip-margin to show the focus glow.
Unfortunately, Safari does not support the clip-margin yet
https://bugs.webkit.org/show_bug.cgi?id=236153

384244
 (commit: 2612b00)