highlight SLE BCI being a SLE derivative

[dirkmueller]

Currently the documentation uses "BCI", "SUSE BCI" and "SLE BCI". we should stick to one wording and use that consistently. the suggested word to use is "SLE BCI" which highlights that it is a SLE derivative.

We need to document in the "Why SLE BCI?" documentation then what the qualities you can get from SLE BCI (certifications etc when upgrading to the paid offering).