show "displayable" system folders in folder lists

Gmail1's "displayable folder" logic is already implemented in
the Gmail provider. The UI now assumes 'rawFolders' is already
filtered and suitable for display in list, view, and folder
dialog.

Browsing a label now shows Inbox for inbox conversations.
Conversation view shows Inbox for inbox conversations.

Change-Id: Ib4c08ecb182b74c4067d5e2e898bb501dad605be
3 files changed