Verity: New deployment-time configuration properties

[pnowosie]

⚠️ This is investigative work only and is not going to be merged into master

Closes https://github.com/omgnetwork/private-issues/issues/76

Overview

See mentioned issue 👆

Changes

Allows following configuration properties to be set at deployment time

• SUBMIT_WHEN_N_TXS - submit block if there is C=10k txs already (or wait n-Eth block otherwise),
• SUBMIT_EVERY_NTH - submit a block every nth ethereum blocks,

Testing

Added release_tasks tests.

[pnowosie]

Moved to https://github.com/omgnetwork/elixir-omg/pull/1706