HUE-1027 [core] HDFS trash and restore

Move items to be trashed into /users/<current user>/.Trash/Current/<path>.
HDFS will handle eventual purging of that directory, so we do not worry about
excess directories being created.
HDFS will also handle checkpointing.
Adding timestamp suffixes to paths if they exist in Current directory.
Performs any necessary mkdirs along the way.

Restoration looks at /users/<current user>/.Trash/<timestamps>/<path>.
It moves out of trash, directly to <path>.
Performs any necessary mkdirs along the way.

Testing requires HDFS pseudo cluster to be started with trash enabled.
set fs.trash.interval to 10, which is 10 minutes.

Add option in UI to skip trash.