- Added cancel button to undo saving of items in case
it was started by mistake
- If none of /connector/save* endpoints were called yet,
the button will just exit at saveItems.
- If the connector server has been engaged, hit /connector/cancel
to tell the server to undo this session
- After cancel button is clicked, the connector window is hidden
- Minor style tweaks to fit the cancel buttons on the same
row as tags input and done button

- place the Done and Cancel buttons in the header
- minor re-styling of all buttons in the header
so they look more uniform
- added new svg-s for relevant buttons, deleted unused files
- disclosure button will flip the up/down on each click
- cancel and done button will expand on hover and
change the icon for textual label
- made the entire dialog a bit wider
- do not set explicit height of the dialog using scrollHeight
anymore, just let it expand as much as it needs unless
it leaves outside of the bounds of the screen
- made the dialog a flexbox so that the progress box
with items can expand as much as it needs and then
become scrollable if we run out of space

and no margin after the last visible button in header

Do not show cancel button if the client did not return
supportsSaveCancelling from /ping or if we are saving
to web library.

Instead of an extra checkOnline call

Fixed bug where an error would be thrown in the
end of changeHeadline if there is no target and the
header would not get set.