arcyon task-create: support '--format-id'

Change the default output of 'task-create' to match the style of
'create-revision', i.e. user-friendly output by default and
machine-friendly if requested.

Test Plan:
$ ./precommit.sh
arcyon: support 'format-url' for some commands

When creating or updating revisions and tasks, it may be useful to print
out just the url of the new/updated item for consumption by wrapper
scripts.

Added to
- arcyon create-revision
- arcyon update-revision
- arcyon task-create

Test Plan:
$ ./precommit.sh
Try each of the --format-* options for the affected commands
Arcyon:refactor, extract phlcon_user.UserPhidCache

Factor out the code for mapping username->PHID from 'arcyon query' and
'arcyon create-revision' as we're also going to need it in
'arcyon task-create'.

Test Plan:
$ ./precommit.sh
tried creating revision with different reviewers and querying for
revisions of different authors.
arcyon: fix grammar in summary message, whitespace
arcyon task-create: support 'owner', 'ccs'

Add support for the 'owner' and 'ccs' fields to 'arcyon task-create'.

Test Plan:
$ ./precommit.sh
Tried creating tasks with various owners, ccs