PDO defaults

[mcbridejc]

Allow PDO default settings to be specified in device config, e.g.:

[pdos]
num_rpdo = 4
num_tpdo = 4

# Setup TPDO1 to be enabled by default, transmitting on $NODEID + 0x200
[pdos.tpdo.1]
enabled = true
cob_id = 0x200
add_node_id = true
transmission_type = 254
mappings = [
    { index=0x2000, sub=1, size=32 },
]

This simple feature became more complicated -- and sprawled into 39 files! -- because the defaults are a function of the node ID, and that has implications for how/when defaults are initialized and persisted object values are loaded. Up to now, object defaults have just been set in object initializers, that will have to change in the future for all objects (see #35). For now, PDO defaults are initialized by the Node, and this means that persisted values cannot be loaded until after the node is created, so I went ahead and added callbacks for ResetApp and ResetComm, as well as all of the other NMT state changes. Applications that support persistent object stored should read the persisted objects in the ResetApp and ResetComm callbacks.

The callback structure is also adjusted, and callbacks are no longer required to have static lifetimes. Instead of passing the CAN message sender callback to Node::process, it is included in the callbacks during initialization.

Other breaking changes

• the node_configuration mod is moved from zencan-client to zencan-common.
• cob is changed to cob_id in node configuration files / PdoConfig.
• zencan_common::objects::PdoMapping renamed to PdoMappable to distinguish it from zencan_copmmon::pdo::PdoMapping.