Form validation on login page

Using ngMessages, adds form validation to login page. Also creates a
directive, hasError, to be used to validate form field by passing
in a boolean. Thi

Form validation on login page

Using ngMessages, adds form validation to login page. Also creates a
directive, hasError, to be used to validate form field by passing
in a boolean. This is a proposed pattern to be used moving forward,
as form validation is added to additional pages.

Validation error messages are shown on $touched and on submit.
Unreachable Server and Invalid username and password error messages
remain until input is no longer $pristine after form submission.

In addition, this removes unneeded and unused css styling

Resolves openbmc/phosphor-webui#47

Change-Id: I7a067af67ac74d4cf2977d10f66445720ecae9eb
Signed-off-by: beccabroek <beccabroek@gmail.com>

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