A&A support: better compilation fix

A&A support: better compilation fix

- revert the previous layout change where inputenc was mentioned. This was not wrong but too intrusive for a change in branch
- mention that the aa class loads natbib to avoid compilation errors
- aa_sample.lyx: the aa package contains an outdated an customized version of natbib.sty. This file only woks with aa, but breaks the compilation of many other files on your system, therefore remove the bibliography and replace it by BibTeX; also clean up the preamble and add a note about the encoding
- aa.lyx: add a note about the encoding and set it in the document settings