Add confirmation modal component

This ticket adds a simple confirmation modal that can be used in
place of window.confirm().

Closes COUCHDB-2445
harden bulkDelete test

sometimes it has false positives
Make deleteDatabase test in Nightwatch more specific
Refactor CSS for pane layout

 - remove JS hack to have fixed elements on a certain size,
   elements now use position absolute/relative and floating

 - header, breadcrumbs and panes do not overlap anymore, which
   lead to alot of bugs like visible but not clickable buttons
   and problems when trying to add new elements to the header

 - header is now aligned with navigantion/burger-height
   (both 64px)

 - componentize footer for all_dbs page

Closes: COUCHDB-2320 COUCHDB-2271 COUCHDB-2471 COUCHDB-2482
with-tabs-sidebar
wip
componentize all-db-footer
fix sidebar
Small adjustments for new header size
fix issues from review
fix cog
fix query-options-buttons, unify common used css
size of database icon
wip
fix border and shadow borders
readd border to queryoptions button
fix arrow on api navbar
adjust breadcrumb first child size
remove duplicated borders
fix typeahead