Added client string to configuration

Clients can set their own client string which will be send to connected
peers during the handshake.
Added AddFunds method
Commented out code due to rewrite vm
Comply to Callee structure
Closures and vm based on closures

Status: Work in progress
Fixed issue with stack where it sliced of the wrong values
Moved code around
Comply to Callee interface
Added encoder interface
Some minor updates
Fixed MSTORE and added some more commets
Rewrote opcodes again
Removed caller from tx and added "callership" to account.

Transactions can no longer serve as callers. Accounts are now the
initial callee of closures. Transactions now serve as transport to call
closures.
Added address to account and contract

Contract and account now both have an address field or method for the
sake of simplicity.
New tx methods and added new vm to state manager
Implemented closure arguments
Closure return, arguments fixed. Added proper tests
Changes 'compiler' to work with any type
Removed regular ints from the virtual machine and closures
Removed old VM code