Add /bl alias for /blocklocker
Add support for trapped chests

They unfortunately don't have the Chest MaterialData, but instead use
the default one. Adding a special case for trapped chests fixes this.
Don't ignore empty lines on signs

The line numbers now always match the list indices, which solves a few
bugs with blank lines. Empty lines will be converted to player profiles
with the zero UUID, this is handled by the UUID conversion code.