Remove restriction to `*.pdf` files

[Fighter456]

Problem

Currently the source folder selection is restricted to *.pdf - documents. Therefore the program is unable to process non-pdf files.

PatternFileMover/PatternFileMover/Form1.cs

Line 51 in 3bf7c40

string[] files = Directory.GetFiles(this.sourceDirectory, "*.pdf");

(Possible) Solution

Make it possible to add affected file extensions to the list of name associations and set *.pdf as the default value and remove these hard-coded programmatically restriction.