Unit test all the functions of OSTPrime.

[deepesh-kn]

This story cover the following.

• Add unit tests for all the functions. (Please refer Utilitytoken test in openst-contract)
• Test of wrap and unwrap is already part of another ticket.
• Add Error message for requires if it is missing.

[schemar]

Please make sure that you fully test claim and redeem (wrap and unwrap).

Specifically:

// Line 138 should probably not be `transfer`, but rather:
transferFrom(msg.sender, address(this), _amount);

// Line 163 should probably not be `transferFrom`, but rather:
transfer(msg.sender, _amount);

Looks like a bug.