add ability to change location of .hugin

[mkaut]

Add an possibility to change location or file name of the ini-file ~/.hugin (on Linux), for ex. using a command line option.
The reason is that there is another program called Hugin (www.hugin.com), which actually pre-dates your Hugin, and it uses the same ini-file - so they mess it up for each other. I have asked them and the path ~/.hugin is hard-coded there, so my only hope for using both is to change it in your Hugin.

Thanks

[Bruno Postle (brunopostle)]

Yes, a command-line option to specify an alternative configuration file would also be useful for debugging and for users who would like to use multiple configurations.

[tmodes (tmodes)]

The default branch is now using the XDG specification to store the settings (when compiled with wxWidgets 3.1.1 or later).
With this it is possible to change the location of the setting file by setting environment variable XDG_CONFIG_HOME.