This commit removes BIP70 support. Since this was the only thing our
payment sernver supported (we had previously dropped support for
bitcoin: urls) I also dropped all the paymentrequest logic.
* separate completion for bitcoind and bitcoin-cli
* remove RPC support from bitcoind completion
* add completion for bitcoin-tx and bitcoin-qt
* rely on autoloading of completions
* Support new rpc commands.
* Several commands now take an optional boolean includeWatchonly argument.
* "help" now has section headers, ignore them when compiling list of commands.