Fix account button setup order

Data-source does not need to be re-set to run the
did-set operations. Just ensure KVO is set up
properly before re-setting button type.

Also, don't guard button type setting.
Fixup updating account button name label

Properly resize label and clean up some redundant
logic.
Reorganize and rename account button updating
Refactor and harden type-driven hiding in account button
Add bar-button-item support in account button

Button-item resizing doesn't play well with
AutoLayout, so we override sizeThatFits to
manually provide the size on each layout.

Also update sample app integration.
Add convenience initializer for account button

Lessen the end user's app delegate code as much
as possible.
Merge pull request #20 from 3dna/peng/refine-account-button-2

Refine account button #2

Addresses previous, incomplete addition of
button-type driven layouts. Adds some conveniences
for easier integration. Includes minor cleanup. No
new user-facing functionality.