Restriction on "send requests" for service taker

[alper-turgal]

As a service taker, I shouldn't send a second request for the same offer.

[alper-turgal]

• [x] Make the "send" button conditional in all_offers_detail.html
• [x] Add a note about the status to the all_offers_detail.html
• [x] Add condition to the view function
• [x] Test
• [x] Fixed