Update fflib_SObjectSelector.cls

Changed the default value of getOrderBy() as not all objects have a 'Name' field (e.g. OpportunityContactRole, CampaignMember).
Update fflib_SObjectDescribe.cls

Added getNameField() method.
Update fflib_SObjectDescribeTest.cls

Added test method for fflib_SObjectDescribe.getNameField().
Update fflib_SObjectSelector.cls

Added a lazy loaded fflib_SObjectDescribe property to handle internal describe calls, updated getOrderBy() to use the name field of the object if present, otherwise the CreatedDate field.
Update fflib_SObjectDescribe.cls

Changed getNameField() to use a lazy loaded private property.
Update fflib_SObjectSelector.cls

Minor formatting changes to conform with the code style of the rest of the library.
Update fflib_SObjectDescribe.cls

Removed the nameField property and put it inline in getNameField().
Update fflib_SObjectSelector.cls

Removed orderBy property and put inline in getOrderBy().
Update fflib_SObjectDescribe.cls

Changed the type of nameField from String to Schema.SObjectField so that the code actually compiles.
Merge pull request #15 from adtennant/patch-1

Update fflib_SObjectSelector.cls getOrderBy() default behaviour