Implement borrow functionality

[aly76]

Added the ability to borrow books, as specified in Issue #16, and track due date #19.

• Created the Borrow Log object, which records book copies lent to contacts.
• Created Due Date formula field in Borrow Log, which calculates as two weeks from the borrow date.
• Implemented the borrow action, which creates a new Borrow Log record after the availability of the book copy has been validated. A process then updates the copy status to 'Loaned'.
• Improved display format of ISBN field by changing it to a text field.

Refer to commit 6b01ae2 message for further details.

[aly76]

Conflict resolution in progress...

[aly76]

Submitted another pull request with a cleaner commit history that does not duplicate Book, Book Copy and Admin Permission Set commits.