CSS cleanup and improvements.

Moved forms styles from page.less to separate form.less file.
Removed "Remember Me Popup" styles from page.less (just used in persistent login) and replaced with a tooltip. Overriden: persistent/remember_me_tooltip.phtml.
Minor css adjustments and cleanup in page.less.
Minor css fix in login.less.
Defined .heading1() in global.less.
ChangeLog and demo link.