Fix toString for some CampaignFilters (#11)

prevent unnecessary usage of getAffiliateSites method (#10)

* Update TradeTrackerClient.php

Add Timezone to CampaignInfo (#9)

* Update CampaignInfoMapper.php

* Update CampaignInfo.php

Added default return type array for getCategories in CampaignCategory

* Update CampaignCategory.php

Removed array typecast on getCategories. If a category has no sub categories we where getting errors like this:
Symfony\Component\Debug\Exception\FatalThrowableError: Return value of Hypeit\TradeTracker\Model\CampaignCategory::getCategories() must be of the type array, null returned

* Update CampaignCategory.php

Make response getCategories backwards compatible

* Update CampaignCategory.php

return type restriction on getCategories

Merge pull request #7 from hypeit/fixes

fixed constructor for some models

Merge pull request #6 from hypeit/readme

Readme