Made the flipped y-axis on terrain import optional.

Pass a final boolean argument to TerrainBlock::import to control
y-axis flipping. It is enabled by default, since this was the previous
default behavior.

This should be added as an option in the terrain import dialog - see
game/tools/worldEditor/gui/guiTerrainImportGui.gui
Some default particles now have additional defaults for their times[n] array.  This resolves some console warning spam.
Merge pull request #274 from thecelloman/issue225

Resolve issue #225:  Minor Issues From ParticleData Times Change
Added a checkbox to the terrain import GUI and fixed a space.
Relocating the particles image directory out of art/shapes/particles to art/particles.  This should be a more logical and intuitive location.  Relevant managed particle related datablock save location defaults have been adjusted as well.
Merge pull request #278 from thecelloman/relocateparticles

Relocated the particles subdirectory to a more intuitive location.
Merge pull request #268 from eightyeight/terrain-import-flipped

Importing terrain heightmaps flips Y-axis