allow users to change their usernames

[barisusakli]

things to update

'username': username,
'userslug': userslug,

in user hash and

db.setObjectField('username:uid', username, uid);
db.setObjectField('userslug:uid', userslug, uid);

[akhoury]

db.searchRemove('user', {id});
db.searchIndex('user', {username}, {id})

no?

[akhoury]

based on a trial and error session that I had

[barisusakli]

onice one totally forgot search, thanks!