Fast initial synchronisation

The synchronisation is done directly from bitcoind database files.
Here the steps of the process:

- step 1: copy bitcoin leveldb database in tmp directory
- step 2: prepare sqlite database 
- step 3: parse all blocks backward (the position of each block in blk000XX.dat files, are taken from the leveldb index (blocks/index dir)
- step 4: reorder transactions
- step 5: parse transactions
- step 6: delete bitcoind leveldb database from tmp directory

The main function, where these 6 steps are done, is `blocks.initialise_transactions()`:
https://github.com/JahPowerBit/counterpartyd/blob/develop/lib/blocks.py#L1260

Average time to parse a block on an Intel Xeon 3.2Ghz with a 7200 RPM HD is about 0.1s.

**Important**: bitcoind must be stopped before launching this script.

Missing:
- manage `get_tx_info2`
- add a warning/question "stop your bitcoind, this operations takes times, etc... are you sure you want to continue ? y/n"
- make a python lib for all files in `/lib/blockchain/` installable with pip


it's because the `leveldb` python lib "corrupt" the bitcoind database, and you need to reindex your database to repair it. After some search, seems that read options are stored in the database, and bitcoind detect this changes and raise an error. Don't find a way to not change this read options. 
Here I copy only the `leveldb` database, not all `blk000??.dat`files. It's about 2Go for mainnet and the copy take less than 2mn in my dev computer.