Fix Issue #31

The BoxAuthorizationViewController is upside-down on iOS 5.1.1
Add comments for the fix of #31
Convert custom folder picker cell to use standard UITableViewCell views instead of drawRect

These cells are just cells with the style UITableViewCellStyleSubtitle. The subview positioning
is retained.

This patch introduces a UI change: thumbs are displayed at a logical 32x32 instead of a logical
40x40. The thumbs returned by the API are either 32x32 or 64x64. On retina displays we use the
64x64 thumbs and they are displayed at native resolution.
Enable SDK users to localize the folder picker strings
Update cell alphas on setEnabled
Merge pull request #29 from box/ios7/folder-picker

Convert custom folder picker cell to use standard UITableViewCell views instead of drawRect
Merge pull request #32 from porter-liu/master

Fix Issue #31
Enable localization on empty filesize string
Add xccheckout to .gitignore
Set button background images for highlighted state instead of selected state

Eliminates warnings when loading the folder picker.
Fix tests to work with Xcode 5

This is a breaking change. The test script will no longer run with Xcode 4.5.
Merge pull request #35 from gcurtis/fix-tests-squashed

Fix tests to work with Xcode 5
Ensure there is an autoreleasepool properly set up for the API Operation thread

The API Operation thread is long lived and may accumulate memory without this pool.
Under high load, BoxAPIOperations throw assertion failures on start

The executeOperation method in BoxAPIOperation.m throws an assertion
failure if the method runs and the operation is not ready.

BOXAssertFail(@"Operation was not ready but start was called");

This can happen if a dependency is added to the operation between
the time start is called and executeOperation runs on the API
Operation Thread.

* executeOperation is called asynchronously from operation start
* OAuth2 operations are added as dependencies for *all* operations in
  the queue, including those that are already executing
* There is no coordination between operations starting and operation
  dependencies being added.

Proposed solution: Add a class-level lock to BoxAPIOperation.

* All operations should acquire this lock immediately in start.
* The BoxAPIQueueManagers should acquire this lock before adding
  OAuth2Operation dependencies.
* The BoxAPIQueueManagers should only add dependencies to operations
  that are not executing.
Pull setting operations state = executing into start

This allows operations to set that they are executing when we are sure we have the
lock and allows us to safely async the call to execute operation.
Merge pull request #36 from box/high-load-stability

Under high load, BoxAPIOperations throw assertion failures on start
Merge pull request #34 from box/fix-folder-picker-warnings-ios7

Set button background images for highlighted state instead of selected state
Check if operations are ready before setting state to executing

Fixes GH-38. Thanks @udibr
Add the users request/response builders and managers, as well as the user's model
Expose usersManager in BoxSDK and BoxCocoaSDK

Include the new .h files in the framework header, create users manager
when creating sharedSDK singleton.

This commit also includes the new files and tests for the BoxCocoaSDK.