Moving start in config to cache db/file about bridger

[wuminzhe]

@clearloop create a new toml?

[clearloop]

@clearloop create a new toml?

Better to use a rust mod like default.rs with only a static toml string.

pub static default: &str = r###""###;

Because the relative path *.toml is buggy.

[wuminzhe]

read

if there is no cache file
    use default from code
else
    read from cache file
end

write

if redeem all txs of a block successful 
    write the block to cache
end

[hackfisher]

Need to move transactions(pending for redeem action) to db together with start.

bridger/src/pool.rs

Line 53 in 7ab4b90

pub ethereum: Vec<EthereumTransaction>,