fix(css): scope css color variables to pocket extension class name

[anthony-liddle]

Goal

Fixes issue https://github.com/Pocket/extension-save-to-pocket/issues/270

Todos:

• [x] Bump package version
• [x] Remove newly un-needed resets
• [x] Remove global declaration from inputs
• [x] Change scope of color variables from root to .pocket-extension
• [x] Update style declarations on options page
• [x] Increase z-index on doorhanger

Implementation Decisions

Colors are still included on global, but scoped specifically to class names so there wouldn't be any style-bleed.

Removed the globalVariables and the globalReset variables from options.js because they are automatically included in options.html with the build css file: /assets/pocket-save-extension.css

[anthony-liddle]

Submitted to the Chrome store for review. Will merge once it has launched.