implement block entity data and signs, improve Vector3 usage

[Gjum]

• implement block entity data tracking in world
• implement sign placement in interact
• make Vector3 more flexible by allowing dict and iterables (tuple/list) as init argument
• allow iterables (Vector3/tuple/list) as block positions in world
• clean up the event plugin
• add Python 3.5 to CI

Example for accessing sign text: (cc @AndrewBuck)

# in plugin class:
requires = ('world', ...)

# in some handler:
logger.debug('sign text: %s', self.world.get_block_entity_data(sign_pos).lines)

[gamingrobot]

Once the build is fixed I will merge, it all looks good

[Gjum]

ERROR: py35: InterpreterNotFound: python3.5

um, ok I guess ...