system contract improvements

[duelingbenjos]

Description

1. added capabilities for masternodes to :

• vote on transferring any type of token via the dao
• vote on more general proposals ("topic_vote")
• vote on operations which manage streams ("create_stream", "change_close_time", "finalize_stream", "balance_stream","close_balance_finalize","topic_vote")

2. fixed a bug in currency

3. Updated tests

Type of change

Please delete options that are not relevant.

•  Enhancement (simplifying, beautifying, better performance, etc.)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (change that requires code adjustments in other places)
•  Fork needed (fix or feature that requires a resync of blockchain state)

Checklist

• I have performed a self-review of my own code
• I have tested this change in my development environment.
• I have added tests to prove that this change works
• All existing tests pass after this change
• I have added / updated documentation related to this change