kes Move lock structures into new file lock.h

kes  Move lock structures into new file lock.h
kes  Use jcr lock for locking reservations messages rather than
     the reservations lock.
kes  Rename a number of locking functions to make their sense a
     bit more logical (more to be done), also rename a few other
     methods in the DEVICE structure.
kes  Add a good bit of documentation of the SD locking mechanisms
     to src/stored/lock.c
kes  Convert a number of bnet_xx calls to use the new bsock class.