* Remove six for PY2 compatability since our dependencies are not, PY2
is legacy.
* Removed usages of utils from future/past libraries since they are
deprecated. This includes 'from __future__ ...' and 'from past...'
statements.
* Removed compatibility imports for PY2, switched from six imports to
standard library imports.
* Removed utils code blocks that handle operations depending on PY2/3
versions.
* Removed 'from __future__ ...' lines from templates/code generators
* Used PY3 syntaxes in place of PY2 compatible blocks. eg: metaclass
- remove several unnecessary comprehensions from functions that accept a generator.
- Using `[x for x in iter]` causes a list to be built first then passed to the outer function.
- `any` and `all` can take generator instead. This makes memory usage O(1) and actually makes these functions short-circuiting. E.g. if the first condition fails then `all` will immediately return false instead of evaluating all the entries.
- `sum`, `min`, `max` => memory usage become O(1)
- `list`, `set`, `.join()` => roughly halves memory usage, as list is not required to be built.
- lastly, it's two fewer characters to read/think about.
Fix several untranslatable strings
Fix permission issue in communication when changing status
Fix functions in inbox view broken, like Tags View and Likes
Add ability to move emails to another email account
Add status = open in standard filters of communication
Add ability to sort after communication date in communication list
Add indicators for status closed and replied in inbox view
Add new role "Inbox User"
Reorder and regroup some custom buttons in communication form
Show more useful fields in email account list
* [minor] refresh inbox view on mark as read or mark as unread
* [minor] refactor mark as read and mark as unread
* [minor] don't update modified datetime while settings _seen
