Fix #72
Make toxgui installable

Fixes #15
Include math.h for log() (fix for OSX)
Change install path: /usr/bin -> /usr/local/bin
translations/ru: minor improvements
Merge pull request #74 from suhr/translations-ru

translations/ru: minor improvements
Improve Tox ID display in settings

Fixes #42
Release updated russian translation
Add option to disable translations