Add communication between actors and main

Multiple actors will have to communicate between them by sending
transactions to each other so a prototype of this communication is
created here where the main goroutine plays the part of a coordinator.
A OnBlockConnected notification has been added to notify main to stop
transcations when the someBigNumber-th block, after the actors have
started running, has been added in the blockchain.

Other than that, almost every use of log.Fatalf has been dropped to
log.Printf, use of a time-dependant random seed has been added in favor
of purely random address selection inside actors and method BalanceUpdate
has been added for Actors.
Add mining

Mining has been added with the use of the NewMiner function so now a
complete simulation is possible to happen. The way NewMiner works is
that it fires up a fresh btcd instance with --generate and --miningaddr
options enabled (--miningaddr is specified as many times as the number
of actors since every actor uses one of its addresses to collect mining
funds) to mine coins.

Also the communication between actors and the main goroutine has been
upgraded to accomodate actors with insufficient funds.

Finally some refactoring was done in favor of eliminating almost all
globals.
IMPORT PATH MODIFICATION CHANGESET
----------------------------------

Please use this changeset as the first one on top of the conformal codebase.
Note that if there are new imports, they need to be changed as part of this
changeset. In general, use "git rebase" on github.com/conformal's version
and apply this changeset first.