Option: navbar sticks on top of the window

[kennethrioja]

Fix #1120

Summary of changes

• tess.example.yml: you have now sticky_navbar option under feature, set to false by default, when true it allows the header to stick to the top of the window and shrink (animated) a bit while scrolling down
• application.js and application.scss: added the .erb extension to both files to allow <% if TeSS::Config.feature['sticky_navbar'] %>
• _header.hrml.erb: incorporated header_notice to the header class="unified-header"> to allow sticking to the top at anytime

Motivation and context

Not being able to click on the navbar when in the bottom of the window, it is frustrating and 'effortful' to scroll to the top everytime

Checklist

• I have read and followed the CONTRIBUTING guide.
• I confirm that I have the authority necessary to make this contribution on behalf of its copyright owner and agree
  to license it to the TeSS codebase under the
  BSD license.

[fbacall]

I would not toggle the feature this way, since it would involve rebuilding the JS/CSS if the feature is toggled.

Instead you can add a class or data attribute to the header (or body element even) in the ERB templates if the feature is enabled, and then check for that class/attribute dynamically with a JS selector.

[fbacall]

See other comment.

If you add an additional class to the header when the sticky navbar feature is enabled, you can just add the CSS rules to that class and they will be ignored if the feature is not enabled.