Merged install.css with install-rtl.css (it is used only when installing so it...

Merged install.css with install-rtl.css (it is used only when installing so it makes sense to be a separate stylesheet), merged farbtastic.css with farbtastic-rtl.css, see #18314

git-svn-id: https://core.svn.wordpress.org/trunk@18578 1a063a9b-81f0-0310-95a4-ce76da25c4cd