never pass nil to image_tag

In production that results in a not precompiled error
Update robots.txt comments

clarify comments and update permanently moved URL
Merge pull request #4222 from rivendale2010/patch-1

Update robots.txt comments
Merge pull request #4221 from svbergerem/4123-fix-login-short-password

Fix login for short passwords
Merge pull request #4217 from svbergerem/4041-loading-indicator

Add loading indicator on tag pages, remove second one from profile page

Conflicts:
	Changelog.md
Change image to ajax-loader when closing lightbox