POC Venmo Button

Should be converted to use our SDK before hitting prod.
Respect Do Not Track header for Segment.io.
Add segment.io testing credentials.
Add segment.io tracking by user id.
Fix segmentio identify functions for anon and auth'd users.
Fix header format for aspen, not django.
Bypass request object modification and check DNT directly from header.
DNT code pushed into util.
Updated privacy policy to mention segment.io.
we don't need a new hook for DoNotTrack
Add mention of DNT to privacy policy.
Move account actions into <td> to fix alignment bugs
Use Venmo's sdk
only show actually connected accounts. Resolves #2194
Update payday.sh's test mode

To keep up with changes to dev env.
Merge pull request #2375 from gittip/fix-payday-test-mode

Update payday.sh's test mode
Merge pull request #2363 from ivanmushketyk/nonexisting-accounts

Only show actually connected accounts
Bump version to 12.9.6
Bump version to 12.9.6-dev
Merge branch 'master' into add-venmo-button

Conflicts:
	templates/connected-accounts.html