Minor style fixes

This fixes a number of small issues described in:
https://issues.apache.org/jira/browse/COUCHDB-2370:

 - don't truncate all headers if there is space
 - fix font size of active tasks title
 - add more space to the button in config/add-section
 - fix wording after verfying the installation
 - autfocus the add-section-modal in config

Closes COUCHDB-2370