Adding support for adsense

[Poliuk]

Add support for the 3 formats:

• Display units https://support.google.com/adsense/answer/185666
• Text ads https://support.google.com/adsense/answer/185665
• Link units https://support.google.com/adsense/answer/185679

[Poliuk]

We have to take in count the adsense's policy limits for the amount of ads displayed per page.

• https://productforums.google.com/forum/#!topic/adsense/Rl4Y8Wxnrj4
• http://afriwap.com/google-adsense/you-can-now-implement-unlimited-amount-of-ads-per-page-on-adsense/
• https://marketingland.com/google-removes-adsense-3-ads-per-page-limit-focuses-content-ad-balance-189064