Fixed homepage image tile size bug.
Fixed all relative urls using Flask url_for, rather than hardcoded ‘/‘.
Fixed bug where embed_codes with length 0 were being used as valid urls
Merge branch 'develop' into hotfixes

* develop:
  Fixed all relative urls using Flask url_for, rather than hardcoded ‘/‘.
  Fixed homepage image tile size bug.
Merge branch 'hotfixes' into develop

* hotfixes:
  Fixed bug where embed_codes with length 0 were being used as valid urls