Improve UX for bounties posted on behalf of a team

A few times now users (including myself) have hit some confusion and awkwardness when trying to post a bounty (or several in a row) on behalf of a team instead of personally. There might be a quirk when posting several quickly in a row with the "Display As" field swapping. Example user experience:

"There appears to be some sort of issue with the payment form. I believe it occurred because I swapped the "Display as" account and paid too quickly. For a number of the bounties I remade, the account swapped back to my personal account as I was paying for the bounty."

Additionally I think it might be an idea to let users themselves edit the on behalf of / display as on an existing bounty they posted/own. That way it doesn't take a support request to fix that. That seems a regular request and while I just realized I *can* edit the bounty origin that seems somewhat fiddly (easy to screw up) and is certainly more work to put on support that users would probably be happy to do on their own.

Goal of this issue would be:

* Review the existing flow and maybe make the "Display As" more sticky (don't reset between bounties if posting multiple in a session) or at least confirm that no involved input element has any sort of delayed initialization able to cause this sort of confusion
* Clarify any related descriptions in various places of how the "Display As" matters - for instance a bounty posted personally to a team's issue won't show up in the team total. I know I didn't realize that personally for a while
* Provide new functionality somewhere that allows a user to switch the "Display As" on an existing bounty they own to a team they're on.

This could be a useful little improvement yet it seems nicely isolated from everything else, making it a good candidate for somebody getting used to Bountysource. Not that merging things is particularly fast these days, but hopefully that'll improve soon :-)

Start by reviewing the existing bounty posting payment form and the "Display As" flow, including how the selected account behaves when several bounties are posted quickly. Then inspect how users currently edit the bounty origin. Done means the flow is less confusing, related descriptions explain team totals, and owners can switch an existing bounty to an eligible team.

Written by the indexing model from the issue text.