Fixed some remaining issues for PSR-1 compliance

- Moved Illuminate/Container/BindingResolutionException to its own file;
- Moved Illuminate/Encryption/DecryptException to its own file;
- Moved Illuminate/Filesystem/FileNotFoundException to its own file.
Merge pull request #5404 from paulofreitas/psr-1

[4.2] Fixed some remaining issues for full PSR-1 compliance