implement escrow revert

[benjaminbollen]

the funds that are put into escrow on calling OpenSTValue.stake and OpenSTUtility.redeem need to revert to the staker or redeemer after the unlockHeight is surpassed and the funds have not been processed.

Addresses #8

[benjaminbollen]

struggled quite a bit implement the closing pieces of the protocol for v0.9.1 to keep deployment of OpenSTUtility around 8M gas (still high but OK as on utility chain side, not Ethereum mainnet - but I wanted to constrain it at that gas consumption cost);

so an important point for 0.9.2 to move up the priority list is a further gas optimisation structuring of the code.

[benjaminbollen]

rebased on #14 for measuring gas consumption (makes previous branches for gh27 obsolete)