Fix Unicef logo bug

[pauloabreu]

Resume

The Unicef logo in footer are breaking in some server because slashes in url:

/sitestatic//img/UNICEF_footer_Logo_black_en.png <- Broken
/sitestatic/img/UNICEF_footer_Logo_black_en.png <- Working

HAML:

%img.-ml-2(src="{{STATIC_URL}} / img/UNICEF_footer_Logo_black_en.png" class="md:-ml-0")
but {{STATIC_URL}} already have a slash, resulting in /sitestatic//img/UNICEF_footer

The Nyaruka code:

in other cases we can see this pattern: %img(src="{{STATIC_URL}}img/u-report-global-logo-white.png"), which works fine.

Reference

templates/public_base.haml:621
templates/public_base.haml:623
templates/public_base.haml:635 
templates/public_base.haml:637
ureport/settings_common.py:144

Issue: #1062