Defer connection to seed nodes until network is up

This stabilizes the startup wrt network connections significantly.
Merge branch 'develop' of github.com:BitShares/bitshares_toolkit into develop
Switch to Bitcoin's LevelDB fork for Linux and Mac
Update LevelDB options
Merge branch 'develop' of github.com:BitShares/bitshares_toolkit into develop
Fix empty response bug in blockchain_market_order_history
Resolve #625
Log chain downloader completion and rate
support higher precision bid/ask prices
Merge branch 'develop' of github.com:BitShares/bitshares_toolkit into develop
Add timestamps to order history
Merge branch 'develop' of github.com:BitShares/bitshares_toolkit into develop
Update submodule
Always force flush wallet key records to disk
Remove extraneous file
Merge branch 'develop' into leveldb
implement FDIC insurance for BitUSD holders
Merge branch 'develop' of github.com:BitShares/bitshares_toolkit into develop
Merge branch 'leveldb' into develop
Add pretty_transaction::expiration_time