STCOR-621: add configuration option for Help link (#1201)
STCOR-621: add configuration option for Help link (#1201)

Adds the ability to specify a the URL used for the Help link in the main
menu bar, by allowing an extra value, config.helpUrl, in
stripes.config.js.  Without this value specified, falls back to the
current default of 'https://docs.folio.org/docs'

To Test:

1. without editing stripes.config.js, deploy.  The link in the main nav
   bar should remain unchanged and active.
2. edit stripes.config.js in include helpUrl in the config section. 
   Point to the URL of your choice
3. deploy, and test.  You should now see the Help icon linking to your
   URL

Refs STCOR-621
folio-org/stripes-core,folio-org/stripes-core,folio-org/stripes-core