Loop now guards all static-address managers against zero block heights: each
constructor returns an error when invoked with a non-positive current height,
and `loopd` validates the height from `GetInfo` before instantiating them.
Tests and helper code were updated accordingly so we fail fast instead of
registering chain notifications with invalid hints.
If Run sets the current height field, it is technically a race between Run and
other methods reading the field. Setting in New is a safer option.
Removed a check that height is not 0 from static address manager.
Make the current height an atomic variable in staticaddr/address/manager.go and
in staticaddr/withdraw/manager.go.
Removed the initiation height from staticaddr/deposit/manager.go (not needed).
