Validate name for table with SetNaming extension method

[hherzl]

Validate the table name with SetNaming extension method, avoid duplicated tables in database.

Example:

// First entity
var category = db
    .DefineEntity(new
    {
        Id = 0,
        Name = ""
    })
    .SetNaming("Category")
    ;

// Second entity
var product = db
    .DefineEntity(new
    {
        Id = 0,
        Name = "",
        CategoryId = 0
    })
    .SetNaming("Category") // The 'Category' entity already exists in db instance
    ;