Make renkulab embeddable in other pages

[ableuler]

While renkulab pages (sessions, gitlab) can be embedded within renkulab itself, it is currently not possible to make renkulab easily embeddable into other pages (like another renkulab instance). This could easily be achieved through a chart value which would specify a host which could be added to this line. And while at it, I think that specifying both self and {{ .Values.ui.baseUrl }} as it's currently done there is superfluous as .Values.ui.baseUrl is self.