Don't munge memo on issue/create of assets, set issuer account

The scanners were replacing a meaningful memo on issue/create asset
transactions with a canned one. Fix this so that the memo is left alone
if it's already set.

Also, the from account was left empty on issue transactions, but the
from account must be the issuer (no one else can issue that asset) so we
can actually set it.
Minor cleanup in wallet::add_contact_account

Make assert failed exceptions human readable, and also don't overwrite
the old private data if the new private data is null.
CLI was incorrectly reporting wallet as being closed because path string to wallet file wasn't set to correct state in create_file. Code is still a bit strange, as we leave the wallet open at end of create_file and then call wallet::open.
Fees can be paid in any asset with an ask

Thei commit provides the implementation, but doesn't test, the ability
to pay transaction fees in any asset for which the lowest ask is able to
fill the fee.
Merge branch 'master' of github.com:BitShares/bitshares_toolkit
Fix wallet_enable_delegate_block_production => wallet_delegate_set_block_production
Improve wallet_account_balance output and remove
wallet_list_unspent_balances (resolves #330)
Do not print nan for invalid pretty-printed percentages
Merge branch 'master' of github.com:BitShares/bitshares_toolkit
stub out some market matching code
Merge branch 'master' of github.com:BitShares/bitshares_toolkit
Fix wallet_account_vote_summary
Move to Unlicense "license"
All regression tests passing
Add genesis_timestamp to blockchain_get_config (resolves #407)
Do not allow negative unlock timeouts and improve unlock error messages
(resolves #392)
fix scanning for market issued assets
Merge branch 'master' of github.com:BitShares/bitshares_toolkit
Accelerate block prop with async revalidation.

Adding a mutex to prevent push_block from being reentrant as the first
step toward making the network code run in its own thread.
[gandalf] Added modified config and batch for win32 build under Jenkins.