Implement borrow and return functionality

[aly76]

Added the ability to borrow and return 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 (Update Book Copy Status) then updates the copy status to 'Loaned'.
• Implemented the ability to return books via a 'Returned' checkbox field on the Borrow Log object. When returned, the Update Book Copy Status process updates the book copy status to 'Available'.

The commits in this pull request were cherry-picked from a branch containing definitions of Book fields, Book Copy, and admin permission set that are mutually exclusive from relevant commits in master.

[kyle-accenture]

The setup of the Burrow action look good.

One thing to note is that if a Burrow Log is manually created accidentally as 'returned' the Update Book Copy Status process will make the Copy both 'Loaned' and un-returnable - but this shouldn't be a problem so long as users only use the 'Burrow' action.

Due Date and Book Title are not yet given view permissions for Admin

[aly76]

Submitted new pull request #25 that addresses the suggested changes.