A user should be able to adjust their loan

[anilhelvaci]

Users should be able to accomplish all of the below functionalities

• [x] To be able to repay some of their debt and receive some collateral back
• [x] To be able to put additional collateral to the loan
• [x] To be able to put additional collateral to the loan and get some more debt
• [x] To be able to get more debt without giving any collateral

[anilhelvaci]

Important test case:

1. User gets a loan
2. Someone else also gets a loan thus the total debt of the pool increases
3. Interest accrues
4. The first user adjusts their loan by giving more collateral and getting more debt

Expected Behavior

• User receives the correct amount from the adjust operation
• The loan's current debt is correct