make the bar download directory configurable

[dumblob]

Currently Sachesi downloads all bar files to the directory where the Sachesi binary resides. This is quite inconvenient on systems which have this binary in read-only directory (e.g. all Linux distributions, BSD systems, and POSIX systems).

What about adding a simple input form or even a separate download dialog window making the download path configurable?

[xsacha]

We changed it to the download dir in: #64
I could have a settings window for this stuff.