Add api parameter to hide all content in a home application.

Change-Id: Ib93458e2b141ccaf44dbe8ad7a0af8e3d350a230
Update Home interface to include showContent().

Change-Id: I93a73950d639f9705f209610185445faa60edaf6
Add showContent implementation to control whether any cards should be added. Handle clickIntents that are not found. Refresh cards when screen is shown.

Change-Id: I8623f492dca553c7b4f347ae4f9b27d16370c2c8