Updated changelog icons.
Removed the mainview code which was used by the old sidebar
Merge pull request #388 from huwshimi/changelog-icons

Updated changelog icons

Added the new icon assets as provided by design.
Merge pull request #389 from hatched/remove-old-code

Removed the mainview code which was used by the old sidebar

All of the functionality that was in mainview was moved to the dispatcher methods so its no longer needed. It appears that there were no test which tested this code directly, only as a side effect of the browser.js instantiating it so those tests are still valid with the new setup.

#### To QA
Do an exploratory QA on items involving the sidebar. Everything should work as expected.
Removed old viewmode and state legacy code from the browser.js
Removed old state code
Fixed failing tests after the unused code removal
Merge pull request #390 from hatched/remove-viewmode-state

Remove viewmode and old state object

This branch removes the old unused viewmode state code and state object. There should be no user facing changes to this, simply code removal

#### To QA
Do some exploratory QA around views changing in the sidebar, everything should work as expected.