Switch to XeTeX

As proposed in https://github.com/AndreyAkinshin/Russian-Phd-LaTeX-Dissertation-Template/issues/7, in order to support modern font technologies and to evade the installation of the PsCyr package, this template has been rewritten to use XeTeX instead of plain old pdflatex.

At the moment only *Synopsis* and *Dissertation* templates have been modified. The *Presentation* template shown some weird incompatibility with XeTeX, but I have not tried to figure out which ones. The other templates are left untouched by me.

One may build the files with xelatex and everything should be fine. As for me, I prefer to use *latexmk*, because it does know when to stop recompiling your sources:

* Dissertation: `latexmk -pdf -pdflatex="xelatex %O %S" dissertation`
* Synopsis: `latexmk -pdf -pdflatex="xelatex %O %S" synopsis`

The resulting PDF files are also included.