Fix log type for sakura and yucca, fix category for yucca (fixes #92)

[joernott]

This fixes the bugs I addressed in issue #92

• There is no "white_sakura_log" or "yellow_sakura_log" item in Oh the Biomes we've gone v1.3.3, but it is "sakura_log" for both of them.
• The yucca palm grows only on sand and drops of oak logs