Revert growth to default true

This was originally true to allow non-configured types to use vanilla behavior, compare to willGrow(TreeType, Block). Specifically it started blocking bonemeal on grass in 1.7.10, as discussed here: http://www.reddit.com/r/Civcraft/comments/2h5112/civcraft_changelog_for_20140922/ckpw1ue
Merge pull request #2 from WildWeazel/patch-2

Revert growth to default true