.deb and .exe should delete installation folder before adding new sources

I had an issue on Windows, which was trying to use old code (importing sqlite3b) whereas this code should not be existing anymore in 0.40.0 versions of Duniter.

I figured out that the installation folder was an interative aggregation of each installation, making a pile of code which may induce various behavior for the program.

So, we should clear the installation folder as a prerequisite to process the real one.