Issue 24 and 27

Adding container slots for repo, file and container size limitations.
Updating UC3 to fail if repo size constraint is violated.
Update main.req
Update main.req
Update main.req

Cleaning up TABS and syntax errors
Update main.req
Updating based on PO feedback

creating 'size' as attribute of Repository and Container
creating 'limit' as attribute of 'Container'
updated UC3/1 to reflect new name
Merge pull request #1 from ataran/Issue-24-and-27

Issue 24 and 27