Add -disablewallet option, to disable wallet support (and BDB)

Conflicts:
	src/init.cpp

Rebased-from: 5d4f3a1f0cbdf52257b41ea09d175c0018ad9434
Litecoin: getworkex: CreateNewBlock() scriptPubKey argument instead of key
qt: GUI support for -disablewallet mode

Rebased-from: 8121047b20f6486bf049e642c3e6ca61682ffdd9