Working theme inheritance

Most of what I changed was in app/views/layouts/application.html.slim the old inheritance logic relied on rails auto-magic helpers that no longer applied for the new school themes as the attributes we were checking are no longer stored in a database.

cpg check out the syntax I know it isn't "correct" but cannot find abother way to make it work.  You cannot just use "not_disable_inheritance" or theme.disable_inheritance? as those helpers do not exist, comparing theme.disable_inheritance == false seems to be actually comparing if the attribute is present not the value of it, rails does not seem to realize this is a boolean attribute so maybe what I am doing is correct or at least the best way for this instance?

I also moved the mixins and variables from the themes to a partial so that they are still processed after you link them from another scss file rather than before.