Reset model configuration

[simon-isler]

Issue:

hotsheet-dummy(dev)> Hotsheet.models.length
=> 4
hotsheet-dummy(dev)> Hotsheet.configure { }
{"Author"=>#<Hotsheet::Configuration::ModelConfig:0x000000010ff72d98 @included_attributes=[:name, :birthdate, :gender, :created_at]>,
 "Post"=>#<Hotsheet::Configuration::ModelConfig:0x000000010ff72c30 @excluded_attributes=[:id, :author_id, :created_at, :updated_at]>,
 "TableNameTest"=>#<Hotsheet::Configuration::ModelConfig:0x000000010ff72b68 @included_attributes=[]>,
 "VeryLongModelNameForOverflowTest"=>#<Hotsheet::Configuration::ModelConfig:0x000000010ff72ac8>}
=> nil
hotsheet-dummy(dev)> Hotsheet.models.length
=> 4