MVP for sponsorship story fields

[lentinj]

• [x] Collect sponsorship_story on sponsor_leaf
• [x] Display in personal donor page.

[jrosindell]

See also #365 though the additional functionality mentioned there is not part of this job.

We already have sponsorship_story and sponsorship_story_level in the DB.

I'd say that the condition for display is that sponsorship_story_level IS NOT NULL.

For now I will propose to hand edit the sponsorship_story_level entries and hand enter stories for existing sponsorships where I can. Hence this job is just a case of collecting in the sponsor leaf page and displaying in personal page.

[lentinj]

The above adds the field to sponsor_leaf, it probably needs some editorial work on the text, especially in relation with the "Extra text" field (I'm not sure what I'd put in each).

Displaying in donor_list already happens.