Adjust z-index to keep fullscreen above inspector

- The inspector is set to jump z-indexes up to 999 which causes it to overlay
the browser views all set to 1/2.
- I investigated the current 'stack' and most of the indexes are set to <20
and > 1000, so adjusted the inspectors to sit in the middle around 500, made
the browser views just over that at 600. 
- Verified all notifications, overlays, etc are > 600 (they're at 1000 and
                higher)

So general rule of thumb is basic things < 100, floating things at 500+,
overlay things > 1000.

Audit from grepping for z-indexes:

lib/views/browser/browser-icon.less:    z-index: 10;
lib/views/browser/bws-searchbox.less:      z-index: 15;
lib/views/browser/charm-full.less:        z-index: 10;
lib/views/browser/charm-token.less:            z-index: 10;
lib/views/browser/main.less:    z-index: 1;
lib/views/browser/main.less:    z-index: 2;
lib/views/browser/overlay-indicator.less:    z-index: 999;
lib/views/cookies.less:    z-index: 100;
lib/views/juju-inspector.less:            z-index: 1;
lib/views/juju-inspector.less:                z-index: 0;
lib/views/juju-inspector.less:                z-index: 2;
lib/views/stylesheet.less:    z-index: 10;
lib/views/stylesheet.less:    z-index: 9999;
lib/views/stylesheet.less:    z-index: 10;
lib/views/stylesheet.less: z-index: 100;
/** This is the inspector stuff here v **/
lib/views/stylesheet.less:    z-index: 999;
lib/views/stylesheet.less: z-index: 0;
lib/views/stylesheet.less: z-index: 2;
lib/views/stylesheet.less: z-index: 2;
lib/views/stylesheet.less:    z-index: 10000;
lib/views/stylesheet.less:    z-index: 10001;

R=gary.poster, benjamin.saller
CC=
https://codereview.appspot.com/13347043