[ChromeOS] Reland - Make WebUI login use only needed resources.

[ChromeOS] Reland - Make WebUI login use only needed resources.

So that we speed up a bit in boot.

For OOBE, use chrome://oobe that has everything. For login case, use chrome://oobe/login which only loads account picker, gaia, user image select and offline message.

- Create login.html etc based on oobe.html etc with OOBE only stuff removed;
- Move core OOBE js logic into DisplayManager so that it could be shared;
- Move header bar stuff into its own files;
- Removed non Gaia signin since it seems no longer needed;
- Also removed login_ui files since they are no longer in use;

BUG=chromium-os:20187
TEST=We should speed up about 200ms in boot, resulting in about 380ms delay after this change.
[email protected]

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=102077