Fix public member names of RPC::Context.

Conflicts:
	src/ripple/rpc/handlers/AccountTx.cpp
	src/ripple/rpc/handlers/AccountTxOld.cpp
	src/ripple/rpc/handlers/Ledger.cpp
	src/ripple/rpc/handlers/LedgerData.cpp
	src/ripple/rpc/handlers/RipplePathFind.cpp
	src/ripple/rpc/handlers/ServerInfo.cpp
	src/ripple/rpc/handlers/ServerState.cpp
	src/ripple/rpc/handlers/Submit.cpp
	src/ripple/rpc/handlers/Subscribe.cpp
	src/ripple/rpc/handlers/TxHistory.cpp
	src/ripple/rpc/handlers/Unsubscribe.cpp
	src/ripple/rpc/impl/Context.h
Clean up Pathfinder.

* Restrict to 80-columns and other style cleanups.
* Make pathfinding a free function and hide the class Pathfinder.
* Split off unrelated utility functions into separate files.

Conflicts:
	src/ripple/rpc/handlers/RipplePathFind.cpp
Fix pathfinding with multiple issuers for one currency (RIPD-618).
Remove unused, confusing isXRP(Issue) function.

* Not used in codebase.
* Whether an Issue "is XRP" isn't well-defined.