* Add new pixel attributes: SemiSolid and Slippery (the latter is WIP)
* SemiSolid pixels are only solid below the player character. You can walk on
them and up and down SemiSolid slopes, but can freely pass through from the
sides or jump through from below.
* Update the Palette Editor UI to replace the Attributes buttons: instead of
text labels they now have smaller icons (w/ tooltips) for the Solid,
SemiSolid, Fire, Water and Slippery attributes.
* Bugfix in Palette Editor: use cropped (24x24) images for the Tex buttons so
that the large Bubbles texture stays within its designated space!
* uix.Actor.SetGrounded() to also set the Y velocity to zero when an actor
becomes grounded. This fixes a minor bug where the player's Y velocity (due
to gravity) was not updated while they were grounded, which may eventually
become useful to allow them to jump down thru a SemiSolid floor. Warp Doors
needed a fix to work around the bug, to set the player's Grounded(false) or
else they would hover a few pixels above the ground at their destination,
since Grounded status paused gravity calculations.
