Fix sidebar design

- Make height of red & grey items in sidebar equal
- Allow scrolling down to the bottom of the list when window height is small
- Better vertically aligned icons
- Also show brown padding between burger and list when scrolled down

Closes COUCHDB-2402
Fix for group_level not being explicitly passed.

Closes COUCHDB-2412
Added constants.js file to core

Closes COUCHDB-2400
Add New Database now opens in tray, not prompt

- minor CSS update to all trays to increase edge padding

Closes COUCHDB-2398
Remove `rightHeader` from changes view for now

We have a separate filter function in this view. It probably
makes sense to integrate this filter into the right header
function later, but currently the rightHeader with the search for
documents and the query-options-tray does not work with changes and
duplicates the functionality of the filter in this context.

Closes COUCHDB-2397
Fix rendering on view-list after creating a view

AllDocsList is lazily adding subviews in the `beforeRender` method,
which causes that it will throw an error for all methods that
access these subviews from outside before explicitly rendering
the view.

As the beforeRender is adding paging, subviews, and the establish
takes care of our collection, we are fine with just rendering.

After we got this working, we can navigate without a
`trigger: false` and are getting a view on the indexed doc after
creating the view.
Use a constant for pagesize