Use existing evars.rc

[Tobbe]

If an old evars.rc is found it should be parsed and as many values as possible should be used. These values should be the suggestions for the evar config pages.

The evars.rc file should be searched for in the directory LOSI is being installed to and in any other LiteStep folder the installer finds.

Sanity checks should be made on all paths so they actually point to an executable file.