Merge lp://staging/~charlesk/indicator-transfer/rtm-usability-fix into lp://staging/indicator-transfer/14.10

Change the indicator's label to "Files" and only show the indicator if there are unfinished transfers.

== Description of Change

Update label and visibility to match changes listed in <https://docs.google.com/a/canonical.com/document/d/1jHIGzAzf7kFELgOiU9J0Hd9mOa3NzTsnEglLmx_qEfk/edit#>:

1. Change the title from "Transfers" to "Files"

2. Change the visibility behavior s.t. the indicator is only visible when there are incomplete transfers.

== Checklist

> Are there any related MPs required for this MP to build/function as expected? Please list.

No

> Is your branch in sync with latest trunk? (e.g. bzr pull lp:trunk -> no changes)

Yes

> Did the code build without warnings?

Yes

> Did the tests run successfully?

Yes

> Did you perform an exploratory manual test run of your code change and any related functionality?

Yes

> Has your component test plan been executed successfully on emulator or a physical device?

Yes, mako + r68

> Please list which manual tests are germane for the reviewer in this MP.

indicator-transfer/visibility

> Did you link to the checklist URL at https://wiki.ubuntu.com/Process/Merges/Checklists/indicator-transfer to make life easier for reviewers/testers?

Yes