Use better name for saving XaoS saved position configuration

[kanurag94]

Currently XaoS uses .XaoSrc and XaoS.config (on windows) as filenames to save the configuration. This is confusing since Qt also designates XaoS.conf as the file for saving application configuration. We should use a better name for the configuration file instead of .XaoSrc and XaoS.config. May be it would be better have the same name on windows and as well as non windows systems.

[jblang]

Having configuration files ending in rc is a standard convention on Unix-like systems (see for example .bashrc). Also, configuration files begin with a . so that they are hidden by default and don't clutter up the ls output in the user's home directory. I think that changing the name is only a small benefit and has potential downsides of surprising long-time users. At the very least, the old filename should still be read in and processed so it doesn't surprise users who upgrade.