Rename the `memberships` table to `takes`; #2282

`memberships` was a bad name for this table because it's ambiguous with
community memberships. Renaming to `takes` fits the usage we've arrived
at and is parallel to `tips`. Tips and takes! Membership is then an
emergent property of data recorded in the takes table.
minor change (make code more DRY)
add test for MixinTeam.get_members()
fix bug in MixinTeam.get_members()
Moving initial data over to the account tab
Switching account tab to col0 and moving bank account information
Useless checking
no it doesn't
reformat & restructure the worst parts of account.js
cleanup
there's no need to empty the session header

don’t set it, and it won’t be there
short-circuit auth checks when loading assets

so we don’t needlessly hit the DB
set CSRF token expiry to a week instead of a year
fix failing test
more appropriate error code
small refactoring
don't generate a csrf token if we're not going to use it
remove duplicate JSON simplates
fix URLs of JSON endpoints in account.js
Merge pull request #2323 from gittip/account-tab

Account Tab