settings for newtab/home replacement

[tborychowski]

parent: #52
Allow users to choose whether they want to replace the newtab, homepage, both or none.
This would also require the extension to add a button to the addon toolbar, which would open its page.

Tasks

• add extension button to the toolbar (example extension)
• add settings to allow the user to select pages for newtab & homepage (perfect home | about:blank | about:newtab | custom url)
• redirect from newtab/homepage to the correct location