Don't get blockClicked in air click PlayerInteractEvent handling

Signed-off-by: Ross Allan <rallanpcl@gmail.com>
Make PluginClassLoader threadsafe, fixes #817

Signed-off-by: Ross Allan <rallanpcl@gmail.com>
Merge pull request #823 from nallar/master

PR #821 for 1.5 - Fix #817, avoid chunkloading in CraftEventFactory when loadChunkOnProvideRequest is enabled