Archetype: build bootstrap/content module conditionally

The archetype contains two bootstrap modules, "configuration" and "content". Purpose behind this is that bootstrap resources in "configuration" are supposed to be bootstrapped into DTAP, while bootstrap resources in "content" should not affect TAP, but provide demo content locally only.

Most project I'm dealing with therefore define a "local" profile to build and package the "content" module only when the "local" profile is activated.

Currently, the archetype (both the legacy archetype and the Essentials archetype) include the content module unconditionally. To make the purpose of the division into two modules more clear, the content module should be moved under the control of the "local" profile, and the README.txt should be updated to reflect this.