Friendly URL for user profile

[tonylampada]

User profile URLs have the user id in it, like: http://freedomsponsors.org/core/user/2/tonylampada

It would be better to use something like:
http://freedomsponsors.org/user/tonylampada

This will have a few impacts:

• UserInfo.screenName will have to be copied to Use.username
• But we must make sure that it's a valid username first.
• We must also make sure that it's unique
• And me must give the current users a time window to change it (it will be immutable after that
• After that we delete screenName from the db.

[tonylampada]

I'm starting this:

• Create a way for users to change username, once.
• Create a task that:
  • Copies UserInfo.screenName to Use.username (removing invalid characters / and de-duplicating if needed)
  • Send an email to users explaining that their usernames have been changed and why, and how it's gonna work. Explain they have 3 months to do so. Then point them the URL where they can change it if they want. Once.
  • When there 15 days left, need to send another email reminding the users who didn't.
• Replace all usages of screenName for username
• Refactor user creation/edition accordingly
• 3 months later, disable the feature.

[tonylampada]

I have a feeling this branch is ready to go. I'll just feel like I need to add a few more tests to it.

[tonylampada]

After a few hiccups, all the necessary data migrations were ran, and (almost) all necessary emails were sent. This is almost done...

[tonylampada]

OK, now it's done. Doesn't look like much, but this has annoyed for a long time, I'm glad I finally did this :-)

People are already changing their usernames.