Unnecessary purges on User model change

[di]

Currently right now any time the User model changes, we purge all the cache keys for that user's project.

This includes attribute changes that don't actually affect the project pages, like last_login, password etc.

We should filter out "purge-able" attribute changes and only issue purges when necessary. Said attributes include:

• username
• name
• emails

[ewdurbin]

it also issues an all-projects which purges /simple
* was looking at wrong log :)

[di]

Hmm, shouldn't be...

[ewdurbin]

my bad, sneaky edited my original comment after checking logs more closely.

[brainwane]

Ernest mentioned we need this before launching beta, because otherwise it's so costly to serve users who have many projects each.